[PATCH V2 0/2] Add support to preserve boot config in the DT flow

[PATCH V2 0/2] Add support to preserve boot config in the DT flow

[Vidya Sagar]

Add support to preserve the boot configuration of the PCIe bridges per
host bridge basis based on the presence of the DT flag "preserve-boot-config"
in the respective host bridge node. The existing "linux,pci-probe-only" works
at a system level and can't be used at a single host bridge granularity.
Also, the support for preserving the boot configuration per host bridge basis
is already present for the ACPI based boot flow and this patch series extends
that support for the DT based boot flow.

V2:
* Addressed issues reported by kernel test robot <lkp@intel.com>

Vidya Sagar (2):
  dt-bindings: Add PCIe "preserve-boot-config" property
  PCI: Add support for "preserve-boot-config" property

 Documentation/devicetree/bindings/pci/pci.txt |  4 ++++
 drivers/pci/controller/pci-host-common.c      |  5 ++++-
 drivers/pci/of.c                              | 18 ++++++++++++++++++
 drivers/pci/probe.c                           |  2 +-
 include/linux/of_pci.h                        |  6 ++++++
 5 files changed, 33 insertions(+), 2 deletions(-)

-- 
2.25.1

[PATCH V2 1/2] dt-bindings: Add PCIe "preserve-boot-config" property

[Vidya Sagar]

The existing "linux,pci-probe-only" property applies at a system level
and it is not possible to selectively convey individual host bridge's
requirement w.r.t preserving the boot configuration done by the platform
firmware to the kernel. "preserve-boot-config" addresses that concern
and can be used to preserve the boot configuration for host bridges
selectivey.

Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
---
V2:
* None

 Documentation/devicetree/bindings/pci/pci.txt | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Documentation/devicetree/bindings/pci/pci.txt b/Documentation/devicetree/bindings/pci/pci.txt
index 6a8f2874a24d..0a5ff998cbe8 100644
--- a/Documentation/devicetree/bindings/pci/pci.txt
+++ b/Documentation/devicetree/bindings/pci/pci.txt
@@ -32,6 +32,10 @@ driver implementation may support the following properties:
    root port to downstream device and host bridge drivers can do programming
    which depends on CLKREQ signal existence. For example, programming root port
    not to advertise ASPM L1 Sub-States support if there is no CLKREQ signal.
+- preserve-boot-config:
+   If present this property specifies that this host bridge is already
+   configured by the platform firmware and the OS doesn't need to reconfigure
+   it again.
 
 PCI-PCI Bridge properties
 -------------------------
-- 
2.25.1

Re: [PATCH V2 1/2] dt-bindings: Add PCIe "preserve-boot-config" property

[Rob Herring]

On Wed, Jan 10, 2024 at 08:37:24AM +0530, Vidya Sagar wrote:
> The existing "linux,pci-probe-only" property applies at a system level
> and it is not possible to selectively convey individual host bridge's
> requirement w.r.t preserving the boot configuration done by the platform
> firmware to the kernel. "preserve-boot-config" addresses that concern
> and can be used to preserve the boot configuration for host bridges
> selectivey.
> 
> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> ---
> V2:
> * None
> 
>  Documentation/devicetree/bindings/pci/pci.txt | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/pci/pci.txt b/Documentation/devicetree/bindings/pci/pci.txt
> index 6a8f2874a24d..0a5ff998cbe8 100644
> --- a/Documentation/devicetree/bindings/pci/pci.txt
> +++ b/Documentation/devicetree/bindings/pci/pci.txt
> @@ -32,6 +32,10 @@ driver implementation may support the following properties:
>     root port to downstream device and host bridge drivers can do programming
>     which depends on CLKREQ signal existence. For example, programming root port
>     not to advertise ASPM L1 Sub-States support if there is no CLKREQ signal.
> +- preserve-boot-config:
> +   If present this property specifies that this host bridge is already
> +   configured by the platform firmware and the OS doesn't need to reconfigure
> +   it again.

Anything new must be a schema.

Don't create something new to workaround the problem. Extend the 
existing support. For this, make "linux,pci-probe-only" allowed in host 
bridge nodes. Yeah, there's the issue that this property sets a global 
flag, but I'd imagine the PCI maintainers would agree that some flags 
should/could be per bus.

Rob

[PATCH V2 2/2] PCI: Add support for "preserve-boot-config" property

[Vidya Sagar]

Add support for "preserve-boot-config" property that can be used to
selectively (i.e. per host bridge) instruct the kernel to preserve the
boot time configuration done by the platform firmware.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
---
V2:
* Addressed issues reported by kernel test robot <lkp@intel.com>

 drivers/pci/controller/pci-host-common.c |  5 ++++-
 drivers/pci/of.c                         | 18 ++++++++++++++++++
 drivers/pci/probe.c                      |  2 +-
 include/linux/of_pci.h                   |  6 ++++++
 4 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
index 6be3266cd7b5..d3475dc9ec44 100644
--- a/drivers/pci/controller/pci-host-common.c
+++ b/drivers/pci/controller/pci-host-common.c
@@ -68,13 +68,16 @@ int pci_host_common_probe(struct platform_device *pdev)
 
 	of_pci_check_probe_only();
 
+	bridge->preserve_config =
+		of_pci_check_preserve_boot_config(dev->of_node);
+
 	/* Parse and map our Configuration Space windows */
 	cfg = gen_pci_init(dev, bridge, ops);
 	if (IS_ERR(cfg))
 		return PTR_ERR(cfg);
 
 	/* Do not reassign resources if probe only */
-	if (!pci_has_flag(PCI_PROBE_ONLY))
+	if (!(pci_has_flag(PCI_PROBE_ONLY) || bridge->preserve_config))
 		pci_add_flags(PCI_REASSIGN_ALL_BUS);
 
 	bridge->sysdata = cfg;
diff --git a/drivers/pci/of.c b/drivers/pci/of.c
index 51e3dd0ea5ab..ed3c0dd9804e 100644
--- a/drivers/pci/of.c
+++ b/drivers/pci/of.c
@@ -258,6 +258,24 @@ void of_pci_check_probe_only(void)
 }
 EXPORT_SYMBOL_GPL(of_pci_check_probe_only);
 
+/**
+ * of_pci_check_preserve_boot_config - Return true if the boot configuration
+ *                                     needs to be preserved
+ * @node: Device tree node with the domain information.
+ *
+ * This function looks for a property called "preserve-boot-config" for a given
+ * PCIe controller's node and returns true if found. Having this property
+ * for a PCIe controller ensures that the kernel doesn't re-enumerate and
+ * reconfigure the BAR resources that are already done by the platform firmware.
+ *
+ * Return: true if the property exists false otherwise.
+ */
+bool of_pci_check_preserve_boot_config(struct device_node *node)
+{
+	return of_property_read_bool(node, "preserve-boot-config");
+}
+EXPORT_SYMBOL_GPL(of_pci_check_preserve_boot_config);
+
 /**
  * devm_of_pci_get_host_bridge_resources() - Resource-managed parsing of PCI
  *                                           host bridge resources from DT
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 795534589b98..79d0ac34f567 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -3085,7 +3085,7 @@ int pci_host_probe(struct pci_host_bridge *bridge)
 	 * ioport_resource trees in either pci_bus_claim_resources()
 	 * or pci_bus_assign_resources().
 	 */
-	if (pci_has_flag(PCI_PROBE_ONLY)) {
+	if (pci_has_flag(PCI_PROBE_ONLY) || bridge->preserve_config) {
 		pci_bus_claim_resources(bus);
 	} else {
 		pci_bus_size_bridges(bus);
diff --git a/include/linux/of_pci.h b/include/linux/of_pci.h
index 29658c0ee71f..ba5532005125 100644
--- a/include/linux/of_pci.h
+++ b/include/linux/of_pci.h
@@ -13,6 +13,7 @@ struct device_node *of_pci_find_child_device(struct device_node *parent,
 					     unsigned int devfn);
 int of_pci_get_devfn(struct device_node *np);
 void of_pci_check_probe_only(void);
+bool of_pci_check_preserve_boot_config(struct device_node *node);
 #else
 static inline struct device_node *of_pci_find_child_device(struct device_node *parent,
 					     unsigned int devfn)
@@ -26,6 +27,11 @@ static inline int of_pci_get_devfn(struct device_node *np)
 }
 
 static inline void of_pci_check_probe_only(void) { }
+
+static inline bool of_pci_check_preserve_boot_config(struct device_node *node)
+{
+	return false;
+}
 #endif
 
 #if IS_ENABLED(CONFIG_OF_IRQ)
-- 
2.25.1

Re: [PATCH V2 2/2] PCI: Add support for "preserve-boot-config" property

[Bjorn Helgaas]

On Wed, Jan 10, 2024 at 08:37:25AM +0530, Vidya Sagar wrote:
> Add support for "preserve-boot-config" property that can be used to
> selectively (i.e. per host bridge) instruct the kernel to preserve the
> boot time configuration done by the platform firmware.
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> ---
> V2:
> * Addressed issues reported by kernel test robot <lkp@intel.com>
> 
>  drivers/pci/controller/pci-host-common.c |  5 ++++-
>  drivers/pci/of.c                         | 18 ++++++++++++++++++
>  drivers/pci/probe.c                      |  2 +-
>  include/linux/of_pci.h                   |  6 ++++++
>  4 files changed, 29 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
> index 6be3266cd7b5..d3475dc9ec44 100644
> --- a/drivers/pci/controller/pci-host-common.c
> +++ b/drivers/pci/controller/pci-host-common.c
> @@ -68,13 +68,16 @@ int pci_host_common_probe(struct platform_device *pdev)
>  
>  	of_pci_check_probe_only();
>  
> +	bridge->preserve_config =
> +		of_pci_check_preserve_boot_config(dev->of_node);

Thanks for leveraging the existing "preserve_config" support for the
ACPI _DSM.  Is pci_host_common_probe() the best place for this?  I
think there are many DT platform drivers that do not use
pci_host_common_probe(), so I wonder if there's a more generic place
to put this.

I see Rob's concern about adding "preserve-boot-config" vs extending
"linux,pci-probe-only" and I don't really have an opinion on that,
although I do think the "pci-probe-only" name is not as descriptive as
it could be.  I guess somebody will argue that "preserve_config" could
be more descriptive, too :)

Bjorn

Re: [PATCH V2 2/2] PCI: Add support for "preserve-boot-config" property

[Vidya Sagar]

On 1/12/2024 10:28 PM, Bjorn Helgaas wrote:
> External email: Use caution opening links or attachments
> 
> 
> On Wed, Jan 10, 2024 at 08:37:25AM +0530, Vidya Sagar wrote:
>> Add support for "preserve-boot-config" property that can be used to
>> selectively (i.e. per host bridge) instruct the kernel to preserve the
>> boot time configuration done by the platform firmware.
>>
>> Reported-by: kernel test robot <lkp@intel.com>
>> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
>> ---
>> V2:
>> * Addressed issues reported by kernel test robot <lkp@intel.com>
>>
>>   drivers/pci/controller/pci-host-common.c |  5 ++++-
>>   drivers/pci/of.c                         | 18 ++++++++++++++++++
>>   drivers/pci/probe.c                      |  2 +-
>>   include/linux/of_pci.h                   |  6 ++++++
>>   4 files changed, 29 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
>> index 6be3266cd7b5..d3475dc9ec44 100644
>> --- a/drivers/pci/controller/pci-host-common.c
>> +++ b/drivers/pci/controller/pci-host-common.c
>> @@ -68,13 +68,16 @@ int pci_host_common_probe(struct platform_device *pdev)
>>
>>        of_pci_check_probe_only();
>>
>> +     bridge->preserve_config =
>> +             of_pci_check_preserve_boot_config(dev->of_node);
> 
> Thanks for leveraging the existing "preserve_config" support for the
> ACPI _DSM.  Is pci_host_common_probe() the best place for this?  I
> think there are many DT platform drivers that do not use
> pci_host_common_probe(), so I wonder if there's a more generic place
> to put this.
My understanding is that pci_host_common_probe() is mainly used in
systems where the firmware would have taken care of all the platform
specific initialization and giving the ECAM and 'ranges' info through DT
for the Linux kernel to go ahead and perform the enumeration. This is
similar to ACPI way of handing over the system from firmware to the OS.

If PCIe controllers are getting initialized in the kernel itself, then
pci_host_probe() is called directly from the respective host controller
drivers which is the case with all the DesignWare based implementations
including Tegra194 and Tegra234. In those systems, since the controllers
themselves have come up and gotten initialized in the kernel, resource
assignment has to happen anyway.

> 
> I see Rob's concern about adding "preserve-boot-config" vs extending
> "linux,pci-probe-only" and I don't really have an opinion on that,
> although I do think the "pci-probe-only" name is not as descriptive as
> it could be.  I guess somebody will argue that "preserve_config" could
> be more descriptive, too :)
Honestly I would have liked to repurpose of_pci_check_probe_only() API
to look for "preserve-boot-config" in the respective PCIe controller's
DT node and not "linux,pci-probe-only" in the chosen entry, had it not
for the single usage of of_pci_check_probe_only() in arch/powerpc
/platforms/pseries/setup.c file.
Also FWIW, "linux,pci-probe-only" is not documented anywhere.

Since there is at least one user for of_pci_check_probe_only(), and
combining with the fact that the scope where "linux,pci-probe-only" and
"preserve-boot-config" are used (i.e. chosen entry Vs individual PCIe
controller node), I prefer to have it as a separate option.
Rob, please let me know if you have any strong objections to that?

> 
> Bjorn

Re: [PATCH V2 2/2] PCI: Add support for "preserve-boot-config" property

[Rob Herring]

On Mon, Jan 15, 2024 at 08:02:56PM +0530, Vidya Sagar wrote:
> 
> 
> On 1/12/2024 10:28 PM, Bjorn Helgaas wrote:
> > External email: Use caution opening links or attachments
> > 
> > 
> > On Wed, Jan 10, 2024 at 08:37:25AM +0530, Vidya Sagar wrote:
> > > Add support for "preserve-boot-config" property that can be used to
> > > selectively (i.e. per host bridge) instruct the kernel to preserve the
> > > boot time configuration done by the platform firmware.
> > > 
> > > Reported-by: kernel test robot <lkp@intel.com>
> > > Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> > > ---
> > > V2:
> > > * Addressed issues reported by kernel test robot <lkp@intel.com>
> > > 
> > >   drivers/pci/controller/pci-host-common.c |  5 ++++-
> > >   drivers/pci/of.c                         | 18 ++++++++++++++++++
> > >   drivers/pci/probe.c                      |  2 +-
> > >   include/linux/of_pci.h                   |  6 ++++++
> > >   4 files changed, 29 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
> > > index 6be3266cd7b5..d3475dc9ec44 100644
> > > --- a/drivers/pci/controller/pci-host-common.c
> > > +++ b/drivers/pci/controller/pci-host-common.c
> > > @@ -68,13 +68,16 @@ int pci_host_common_probe(struct platform_device *pdev)
> > > 
> > >        of_pci_check_probe_only();
> > > 
> > > +     bridge->preserve_config =
> > > +             of_pci_check_preserve_boot_config(dev->of_node);
> > 
> > Thanks for leveraging the existing "preserve_config" support for the
> > ACPI _DSM.  Is pci_host_common_probe() the best place for this?  I
> > think there are many DT platform drivers that do not use
> > pci_host_common_probe(), so I wonder if there's a more generic place
> > to put this.
> My understanding is that pci_host_common_probe() is mainly used in
> systems where the firmware would have taken care of all the platform
> specific initialization and giving the ECAM and 'ranges' info through DT
> for the Linux kernel to go ahead and perform the enumeration. This is
> similar to ACPI way of handing over the system from firmware to the OS.
> 
> If PCIe controllers are getting initialized in the kernel itself, then
> pci_host_probe() is called directly from the respective host controller
> drivers which is the case with all the DesignWare based implementations
> including Tegra194 and Tegra234. In those systems, since the controllers
> themselves have come up and gotten initialized in the kernel, resource
> assignment has to happen anyway.
> 
> > 
> > I see Rob's concern about adding "preserve-boot-config" vs extending
> > "linux,pci-probe-only" and I don't really have an opinion on that,
> > although I do think the "pci-probe-only" name is not as descriptive as
> > it could be.  I guess somebody will argue that "preserve_config" could
> > be more descriptive, too :)
> Honestly I would have liked to repurpose of_pci_check_probe_only() API
> to look for "preserve-boot-config" in the respective PCIe controller's
> DT node and not "linux,pci-probe-only" in the chosen entry, had it not
> for the single usage of of_pci_check_probe_only() in arch/powerpc
> /platforms/pseries/setup.c file.
> Also FWIW, "linux,pci-probe-only" is not documented anywhere.

Yes, it is[1].

> 
> Since there is at least one user for of_pci_check_probe_only(), and
> combining with the fact that the scope where "linux,pci-probe-only" and
> "preserve-boot-config" are used (i.e. chosen entry Vs individual PCIe
> controller node), I prefer to have it as a separate option.
> Rob, please let me know if you have any strong objections to that?

Didn't I already object?

What's the concern with existing users? There shouldn't be any. If 
"linux,pci-probe-only" appeared in a bridge node, it would have been 
ignored and now would be honored.

Rob

[1] https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/chosen.yaml#L140

Re: [PATCH V2 2/2] PCI: Add support for "preserve-boot-config" property

[Bjorn Helgaas]

On Mon, Jan 15, 2024 at 08:02:56PM +0530, Vidya Sagar wrote:
> On 1/12/2024 10:28 PM, Bjorn Helgaas wrote:
> > On Wed, Jan 10, 2024 at 08:37:25AM +0530, Vidya Sagar wrote:
> > > Add support for "preserve-boot-config" property that can be used to
> > > selectively (i.e. per host bridge) instruct the kernel to preserve the
> > > boot time configuration done by the platform firmware.
> > > 
> > > Reported-by: kernel test robot <lkp@intel.com>
> > > Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> > > ---
> > > V2:
> > > * Addressed issues reported by kernel test robot <lkp@intel.com>
> > > 
> > >   drivers/pci/controller/pci-host-common.c |  5 ++++-
> > >   drivers/pci/of.c                         | 18 ++++++++++++++++++
> > >   drivers/pci/probe.c                      |  2 +-
> > >   include/linux/of_pci.h                   |  6 ++++++
> > >   4 files changed, 29 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
> > > index 6be3266cd7b5..d3475dc9ec44 100644
> > > --- a/drivers/pci/controller/pci-host-common.c
> > > +++ b/drivers/pci/controller/pci-host-common.c
> > > @@ -68,13 +68,16 @@ int pci_host_common_probe(struct platform_device *pdev)
> > > 
> > >        of_pci_check_probe_only();
> > > 
> > > +     bridge->preserve_config =
> > > +             of_pci_check_preserve_boot_config(dev->of_node);
> > 
> > Thanks for leveraging the existing "preserve_config" support for the
> > ACPI _DSM.  Is pci_host_common_probe() the best place for this?  I
> > think there are many DT platform drivers that do not use
> > pci_host_common_probe(), so I wonder if there's a more generic place
> > to put this.
>
> My understanding is that pci_host_common_probe() is mainly used in
> systems where the firmware would have taken care of all the platform
> specific initialization and giving the ECAM and 'ranges' info through DT
> for the Linux kernel to go ahead and perform the enumeration. This is
> similar to ACPI way of handing over the system from firmware to the OS.
> 
> If PCIe controllers are getting initialized in the kernel itself, then
> pci_host_probe() is called directly from the respective host controller
> drivers which is the case with all the DesignWare based implementations
> including Tegra194 and Tegra234. In those systems, since the controllers
> themselves have come up and gotten initialized in the kernel, resource
> assignment has to happen anyway.

acpi_pci_root_create() sets "preserve_config" based on the
DSM_PCI_PRESERVE_BOOT_CONFIG _DSM for all ACPI host bridges.

Similarly, I think we should set "preserve_config" based on the DT
"preserve-boot-config" property for *all* DT-based host bridges,
regardless of where the controller init happens.

  acpi_pci_root_create
    pci_create_root_bus
      pci_alloc_host_bridge
      pci_register_host_bridge
    acpi_evaluate_dsm_typed(DSM_PCI_PRESERVE_BOOT_CONFIG)  <--
    pci_scan_child_bus

  pci_host_common_probe
+   of_pci_check_preserve_boot_config       <-- proposed
    pci_host_probe
      pci_scan_root_bus_bridge
        pci_register_host_bridge
          pci_set_bus_of_node
        pci_scan_child_bus

Maybe we should do both in pci_register_host_bridge()?  E.g., make a
function that sets "preserve_config" based on either the ACPI _DSM or
the DT property, whichever is appropriate, and call it from
pci_register_host_bridge()?

Bjorn

Re: [PATCH V2 2/2] PCI: Add support for "preserve-boot-config" property

[Bjorn Helgaas]

On Wed, Jan 10, 2024 at 08:37:25AM +0530, Vidya Sagar wrote:
> Add support for "preserve-boot-config" property that can be used to
> selectively (i.e. per host bridge) instruct the kernel to preserve the
> boot time configuration done by the platform firmware.
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> ---
> V2:
> * Addressed issues reported by kernel test robot <lkp@intel.com>

I don't think the lkp Reported-by adds useful information in this
case.  I have no idea what lkp actually reported, but I don't think it
reported a bug that is fixed by this patch.

[PATCH V3] PCI: Add support for preserving boot configuration

[Vidya Sagar]

Add support for preserving the boot configuration done by the
platform firmware per host bridge basis, based on the presence of
'linux,pci-probe-only' property in the respective PCIe host bridge
device-tree node. It also unifies the ACPI and DT based boot flows
in this regard.

Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
---
V3:
* Unified ACPI and DT flows as part of addressing Bjorn's review comments

V2:
* Addressed issues reported by kernel test robot <lkp@intel.com>

 drivers/acpi/pci_root.c                  | 12 -------
 drivers/pci/controller/pci-host-common.c |  4 ---
 drivers/pci/of.c                         | 22 ++++++++++++
 drivers/pci/probe.c                      | 46 ++++++++++++++++++------
 include/linux/of_pci.h                   |  6 ++++
 5 files changed, 63 insertions(+), 27 deletions(-)

diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
index 84030804a763..ddc2b3e89111 100644
--- a/drivers/acpi/pci_root.c
+++ b/drivers/acpi/pci_root.c
@@ -1008,7 +1008,6 @@ struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
 	int node = acpi_get_node(device->handle);
 	struct pci_bus *bus;
 	struct pci_host_bridge *host_bridge;
-	union acpi_object *obj;
 
 	info->root = root;
 	info->bridge = device;
@@ -1050,17 +1049,6 @@ struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
 	if (!(root->osc_ext_control_set & OSC_CXL_ERROR_REPORTING_CONTROL))
 		host_bridge->native_cxl_error = 0;
 
-	/*
-	 * Evaluate the "PCI Boot Configuration" _DSM Function.  If it
-	 * exists and returns 0, we must preserve any PCI resource
-	 * assignments made by firmware for this host bridge.
-	 */
-	obj = acpi_evaluate_dsm(ACPI_HANDLE(bus->bridge), &pci_acpi_dsm_guid, 1,
-				DSM_PCI_PRESERVE_BOOT_CONFIG, NULL);
-	if (obj && obj->type == ACPI_TYPE_INTEGER && obj->integer.value == 0)
-		host_bridge->preserve_config = 1;
-	ACPI_FREE(obj);
-
 	acpi_dev_power_up_children_with_adr(device);
 
 	pci_scan_child_bus(bus);
diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
index 6be3266cd7b5..e2602e38ae45 100644
--- a/drivers/pci/controller/pci-host-common.c
+++ b/drivers/pci/controller/pci-host-common.c
@@ -73,10 +73,6 @@ int pci_host_common_probe(struct platform_device *pdev)
 	if (IS_ERR(cfg))
 		return PTR_ERR(cfg);
 
-	/* Do not reassign resources if probe only */
-	if (!pci_has_flag(PCI_PROBE_ONLY))
-		pci_add_flags(PCI_REASSIGN_ALL_BUS);
-
 	bridge->sysdata = cfg;
 	bridge->ops = (struct pci_ops *)&ops->pci_ops;
 	bridge->msi_domain = true;
diff --git a/drivers/pci/of.c b/drivers/pci/of.c
index 51e3dd0ea5ab..7b553dd83587 100644
--- a/drivers/pci/of.c
+++ b/drivers/pci/of.c
@@ -258,6 +258,28 @@ void of_pci_check_probe_only(void)
 }
 EXPORT_SYMBOL_GPL(of_pci_check_probe_only);
 
+/**
+ * of_pci_bridge_check_probe_only - Return true if the boot configuration
+ *                                  needs to be preserved
+ * @node: Device tree node with the domain information.
+ *
+ * This function looks for "linux,pci-probe-only" property for a given
+ * PCIe controller's node and returns true if found. Having this property
+ * for a PCIe controller ensures that the kernel doesn't re-enumerate and
+ * reconfigure the BAR resources that are already done by the platform firmware.
+ * NOTE: The scope of "linux,pci-probe-only" defined within a PCIe bridge device
+ *       is limited to the hierarchy under that particular bridge device. whereas
+ *       the scope of "linux,pci-probe-only" defined within chosen node is
+ *       system wide.
+ *
+ * Return: true if the property exists false otherwise.
+ */
+bool of_pci_bridge_check_probe_only(struct device_node *node)
+{
+	return of_property_read_bool(node, "linux,pci-probe-only");
+}
+EXPORT_SYMBOL_GPL(of_pci_bridge_check_probe_only);
+
 /**
  * devm_of_pci_get_host_bridge_resources() - Resource-managed parsing of PCI
  *                                           host bridge resources from DT
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 795534589b98..d62d1f151ba9 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -15,6 +15,7 @@
 #include <linux/cpumask.h>
 #include <linux/aer.h>
 #include <linux/acpi.h>
+#include <linux/pci-acpi.h>
 #include <linux/hypervisor.h>
 #include <linux/irqdomain.h>
 #include <linux/pm_runtime.h>
@@ -877,6 +878,28 @@ static void pci_set_bus_msi_domain(struct pci_bus *bus)
 	dev_set_msi_domain(&bus->dev, d);
 }
 
+static void pci_check_config_preserve(struct pci_host_bridge *host_bridge)
+{
+	if (&host_bridge->dev) {
+		union acpi_object *obj;
+
+		/*
+		 * Evaluate the "PCI Boot Configuration" _DSM Function.  If it
+		 * exists and returns 0, we must preserve any PCI resource
+		 * assignments made by firmware for this host bridge.
+		 */
+		obj = acpi_evaluate_dsm(ACPI_HANDLE(&host_bridge->dev), &pci_acpi_dsm_guid, 1,
+					DSM_PCI_PRESERVE_BOOT_CONFIG, NULL);
+		if (obj && obj->type == ACPI_TYPE_INTEGER && obj->integer.value == 0)
+			host_bridge->preserve_config = 1;
+		ACPI_FREE(obj);
+	}
+
+	if (host_bridge->dev.parent && host_bridge->dev.parent->of_node)
+		host_bridge->preserve_config =
+			of_pci_bridge_check_probe_only(host_bridge->dev.parent->of_node);
+}
+
 static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 {
 	struct device *parent = bridge->dev.parent;
@@ -971,6 +994,9 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 	if (nr_node_ids > 1 && pcibus_to_node(bus) == NUMA_NO_NODE)
 		dev_warn(&bus->dev, "Unknown NUMA node; performance will be reduced\n");
 
+	/* Check if the boot configuration by FW needs to be preserved */
+	pci_check_config_preserve(bridge);
+
 	/* Coalesce contiguous windows */
 	resource_list_for_each_entry_safe(window, n, &resources) {
 		if (list_is_last(&window->node, &resources))
@@ -3080,20 +3106,18 @@ int pci_host_probe(struct pci_host_bridge *bridge)
 
 	bus = bridge->bus;
 
+	/* If we must preserve the resource configuration, claim now */
+	if (pci_has_flag(PCI_PROBE_ONLY) || bridge->preserve_config)
+		pci_bus_claim_resources(bus);
+
 	/*
-	 * We insert PCI resources into the iomem_resource and
-	 * ioport_resource trees in either pci_bus_claim_resources()
-	 * or pci_bus_assign_resources().
+	 * Assign whatever was left unassigned. If we didn't claim above,
+	 * this will reassign everything.
 	 */
-	if (pci_has_flag(PCI_PROBE_ONLY)) {
-		pci_bus_claim_resources(bus);
-	} else {
-		pci_bus_size_bridges(bus);
-		pci_bus_assign_resources(bus);
+	pci_assign_unassigned_root_bus_resources(bus);
 
-		list_for_each_entry(child, &bus->children, node)
-			pcie_bus_configure_settings(child);
-	}
+	list_for_each_entry(child, &bus->children, node)
+		pcie_bus_configure_settings(child);
 
 	pci_bus_add_devices(bus);
 	return 0;
diff --git a/include/linux/of_pci.h b/include/linux/of_pci.h
index 29658c0ee71f..9e045de3be44 100644
--- a/include/linux/of_pci.h
+++ b/include/linux/of_pci.h
@@ -13,6 +13,7 @@ struct device_node *of_pci_find_child_device(struct device_node *parent,
 					     unsigned int devfn);
 int of_pci_get_devfn(struct device_node *np);
 void of_pci_check_probe_only(void);
+bool of_pci_bridge_check_probe_only(struct device_node *node);
 #else
 static inline struct device_node *of_pci_find_child_device(struct device_node *parent,
 					     unsigned int devfn)
@@ -26,6 +27,11 @@ static inline int of_pci_get_devfn(struct device_node *np)
 }
 
 static inline void of_pci_check_probe_only(void) { }
+
+static inline bool of_pci_bridge_check_probe_only(struct device_node *node)
+{
+	return false;
+}
 #endif
 
 #if IS_ENABLED(CONFIG_OF_IRQ)
-- 
2.25.1

Re: [PATCH V3] PCI: Add support for preserving boot configuration

[Bjorn Helgaas]

On Thu, Feb 22, 2024 at 06:11:10PM +0530, Vidya Sagar wrote:
> Add support for preserving the boot configuration done by the
> platform firmware per host bridge basis, based on the presence of
> 'linux,pci-probe-only' property in the respective PCIe host bridge
> device-tree node. It also unifies the ACPI and DT based boot flows
> in this regard.

> +/**
> + * of_pci_bridge_check_probe_only - Return true if the boot configuration
> + *                                  needs to be preserved

I don't like the "check_probe_only" name because it's a boolean
function but the name doesn't tell me what a true/false return value
means.  Something like "preserve_resources" would be better.  If you
want "probe_only", even removing the "check" would help.

> + * @node: Device tree node with the domain information.
> + *
> + * This function looks for "linux,pci-probe-only" property for a given
> + * PCIe controller's node and returns true if found. Having this property
> + * for a PCIe controller ensures that the kernel doesn't re-enumerate and
> + * reconfigure the BAR resources that are already done by the platform firmware.

This is generic PCI, not PCIe-specific (also in commit log and comment
below).

I think "enumeration" specifically refers to discovering what devices
are present, and the kernel always does that, so drop that part.
Reconfiguring BARs and bridge windows is what we want to prevent.

> + * NOTE: The scope of "linux,pci-probe-only" defined within a PCIe bridge device
> + *       is limited to the hierarchy under that particular bridge device. whereas
> + *       the scope of "linux,pci-probe-only" defined within chosen node is
> + *       system wide.
> + *
> + * Return: true if the property exists false otherwise.
> + */

> +bool of_pci_bridge_check_probe_only(struct device_node *node)
> +{
> +	return of_property_read_bool(node, "linux,pci-probe-only");
> +}
> +EXPORT_SYMBOL_GPL(of_pci_bridge_check_probe_only);

Why does this need to be exported for modules and exposed via
include/linux/pci.h?

> +static void pci_check_config_preserve(struct pci_host_bridge *host_bridge)
> +{
> +	if (&host_bridge->dev) {

Checking &host_bridge->dev doesn't seem like the right way to
determine whether this is an ACPI host bridge.

> +		union acpi_object *obj;
> +
> +		/*
> +		 * Evaluate the "PCI Boot Configuration" _DSM Function.  If it
> +		 * exists and returns 0, we must preserve any PCI resource
> +		 * assignments made by firmware for this host bridge.
> +		 */
> +		obj = acpi_evaluate_dsm(ACPI_HANDLE(&host_bridge->dev), &pci_acpi_dsm_guid, 1,
> +					DSM_PCI_PRESERVE_BOOT_CONFIG, NULL);
> +		if (obj && obj->type == ACPI_TYPE_INTEGER && obj->integer.value == 0)
> +			host_bridge->preserve_config = 1;
> +		ACPI_FREE(obj);
> +	}

Re: [PATCH V3] PCI: Add support for preserving boot configuration

[Vidya Sagar]

On 22-02-2024 22:36, Bjorn Helgaas wrote:
> External email: Use caution opening links or attachments
>
>
> On Thu, Feb 22, 2024 at 06:11:10PM +0530, Vidya Sagar wrote:
>> Add support for preserving the boot configuration done by the
>> platform firmware per host bridge basis, based on the presence of
>> 'linux,pci-probe-only' property in the respective PCIe host bridge
>> device-tree node. It also unifies the ACPI and DT based boot flows
>> in this regard.
>> +/**
>> + * of_pci_bridge_check_probe_only - Return true if the boot configuration
>> + *                                  needs to be preserved
> I don't like the "check_probe_only" name because it's a boolean
> function but the name doesn't tell me what a true/false return value
> means.  Something like "preserve_resources" would be better.  If you
> want "probe_only", even removing the "check" would help.
I'll change it in the next patch.
>> + * @node: Device tree node with the domain information.
>> + *
>> + * This function looks for "linux,pci-probe-only" property for a given
>> + * PCIe controller's node and returns true if found. Having this property
>> + * for a PCIe controller ensures that the kernel doesn't re-enumerate and
>> + * reconfigure the BAR resources that are already done by the platform firmware.
> This is generic PCI, not PCIe-specific (also in commit log and comment
> below).
>
> I think "enumeration" specifically refers to discovering what devices
> are present, and the kernel always does that, so drop that part.
> Reconfiguring BARs and bridge windows is what we want to prevent.
Agree and I'll address it in the next patch.
>> + * NOTE: The scope of "linux,pci-probe-only" defined within a PCIe bridge device
>> + *       is limited to the hierarchy under that particular bridge device. whereas
>> + *       the scope of "linux,pci-probe-only" defined within chosen node is
>> + *       system wide.
>> + *
>> + * Return: true if the property exists false otherwise.
>> + */
>> +bool of_pci_bridge_check_probe_only(struct device_node *node)
>> +{
>> +     return of_property_read_bool(node, "linux,pci-probe-only");
>> +}
>> +EXPORT_SYMBOL_GPL(of_pci_bridge_check_probe_only);
> Why does this need to be exported for modules and exposed via
> include/linux/pci.h?
On a second through, I think it is not required to be exported.
I'll address this also in the next patch.
>> +static void pci_check_config_preserve(struct pci_host_bridge *host_bridge)
>> +{
>> +     if (&host_bridge->dev) {
> Checking &host_bridge->dev doesn't seem like the right way to
> determine whether this is an ACPI host bridge.
Honestly, I couldn't find a clear way to differentiate between an ACPI based
host bridge and a DT based host bridge. Hence, the current code tries to get
the information using both ways and since a system can only be either 
ACPI or
DT based, but one at a time, preserve_config will be set only once (assuming
the system wants it to be set). Let me know if there is a better approach
for this?

I was looking at the way 'external_facing' gets set in both the boot 
flows and
I see that there is no common place for it and the respective flows have 
their
functions separately i.e. pci_acpi_set_external_facing() for ACPI and
pci_set_bus_of_node() for DT.

Thanks,
Vidya Sagar
>> +             union acpi_object *obj;
>> +
>> +             /*
>> +              * Evaluate the "PCI Boot Configuration" _DSM Function.  If it
>> +              * exists and returns 0, we must preserve any PCI resource
>> +              * assignments made by firmware for this host bridge.
>> +              */
>> +             obj = acpi_evaluate_dsm(ACPI_HANDLE(&host_bridge->dev), &pci_acpi_dsm_guid, 1,
>> +                                     DSM_PCI_PRESERVE_BOOT_CONFIG, NULL);
>> +             if (obj && obj->type == ACPI_TYPE_INTEGER && obj->integer.value == 0)
>> +                     host_bridge->preserve_config = 1;
>> +             ACPI_FREE(obj);
>> +     }

Re: [PATCH V3] PCI: Add support for preserving boot configuration

[Bjorn Helgaas]

On Fri, Feb 23, 2024 at 02:48:24AM +0530, Vidya Sagar wrote:
> On 22-02-2024 22:36, Bjorn Helgaas wrote:
> > On Thu, Feb 22, 2024 at 06:11:10PM +0530, Vidya Sagar wrote:

> > > +     if (&host_bridge->dev) {
> > Checking &host_bridge->dev doesn't seem like the right way to
> > determine whether this is an ACPI host bridge.

BTW, I think this condition is *always* true, since it's testing the
address of a member of a struct.

> Honestly, I couldn't find a clear way to differentiate between an
> ACPI based host bridge and a DT based host bridge. Hence, the
> current code tries to get the information using both ways and since
> a system can only be either ACPI or DT based, but one at a time,
> preserve_config will be set only once (assuming the system wants it
> to be set). Let me know if there is a better approach for this?

I'm not sure ACPI and DT will always be mutually exclusive; I think
we're headed toward some combinations, e.g.,
https://lore.kernel.org/linux-pci/1692120000-46900-1-git-send-email-lizhi.hou@amd.com/

But I think "if (ACPI_HANDLE(&host_bridge->dev))" would work.

Bjorn

[PATCH V4] PCI: Add support for preserving boot configuration

[Vidya Sagar]

Add support for preserving the boot configuration done by the
platform firmware per host bridge basis, based on the presence of
'linux,pci-probe-only' property in the respective PCI host bridge
device-tree node. It also unifies the ACPI and DT based boot flows
in this regard.

Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
---
V4:
* Addressed Bjorn's review comments

V3:
* Unified ACPI and DT flows as part of addressing Bjorn's review comments

V2:
* Addressed issues reported by kernel test robot <lkp@intel.com>

 drivers/acpi/pci_root.c                  | 12 -------
 drivers/pci/controller/pci-host-common.c |  4 ---
 drivers/pci/of.c                         | 21 +++++++++++
 drivers/pci/probe.c                      | 46 ++++++++++++++++++------
 include/linux/of_pci.h                   |  6 ++++
 5 files changed, 62 insertions(+), 27 deletions(-)

diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
index 84030804a763..ddc2b3e89111 100644
--- a/drivers/acpi/pci_root.c
+++ b/drivers/acpi/pci_root.c
@@ -1008,7 +1008,6 @@ struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
 	int node = acpi_get_node(device->handle);
 	struct pci_bus *bus;
 	struct pci_host_bridge *host_bridge;
-	union acpi_object *obj;
 
 	info->root = root;
 	info->bridge = device;
@@ -1050,17 +1049,6 @@ struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
 	if (!(root->osc_ext_control_set & OSC_CXL_ERROR_REPORTING_CONTROL))
 		host_bridge->native_cxl_error = 0;
 
-	/*
-	 * Evaluate the "PCI Boot Configuration" _DSM Function.  If it
-	 * exists and returns 0, we must preserve any PCI resource
-	 * assignments made by firmware for this host bridge.
-	 */
-	obj = acpi_evaluate_dsm(ACPI_HANDLE(bus->bridge), &pci_acpi_dsm_guid, 1,
-				DSM_PCI_PRESERVE_BOOT_CONFIG, NULL);
-	if (obj && obj->type == ACPI_TYPE_INTEGER && obj->integer.value == 0)
-		host_bridge->preserve_config = 1;
-	ACPI_FREE(obj);
-
 	acpi_dev_power_up_children_with_adr(device);
 
 	pci_scan_child_bus(bus);
diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
index 6be3266cd7b5..e2602e38ae45 100644
--- a/drivers/pci/controller/pci-host-common.c
+++ b/drivers/pci/controller/pci-host-common.c
@@ -73,10 +73,6 @@ int pci_host_common_probe(struct platform_device *pdev)
 	if (IS_ERR(cfg))
 		return PTR_ERR(cfg);
 
-	/* Do not reassign resources if probe only */
-	if (!pci_has_flag(PCI_PROBE_ONLY))
-		pci_add_flags(PCI_REASSIGN_ALL_BUS);
-
 	bridge->sysdata = cfg;
 	bridge->ops = (struct pci_ops *)&ops->pci_ops;
 	bridge->msi_domain = true;
diff --git a/drivers/pci/of.c b/drivers/pci/of.c
index 51e3dd0ea5ab..f0f1156040a5 100644
--- a/drivers/pci/of.c
+++ b/drivers/pci/of.c
@@ -258,6 +258,27 @@ void of_pci_check_probe_only(void)
 }
 EXPORT_SYMBOL_GPL(of_pci_check_probe_only);
 
+/**
+ * of_pci_bridge_preserve_resources - Return true if the boot configuration
+ *                                    needs to be preserved
+ * @node: Device tree node with the domain information.
+ *
+ * This function looks for "linux,pci-probe-only" property for a given
+ * PCI controller's node and returns true if found. Having this property
+ * for a PCI controller ensures that the kernel doesn't reconfigure the
+ * BARs and bridge windows that are already done by the platform firmware.
+ * NOTE: The scope of "linux,pci-probe-only" defined within a PCI bridge device
+ *       is limited to the hierarchy under that particular bridge device. whereas
+ *       the scope of "linux,pci-probe-only" defined within chosen node is
+ *       system wide.
+ *
+ * Return: true if the property exists false otherwise.
+ */
+bool of_pci_bridge_preserve_resources(struct device_node *node)
+{
+	return of_property_read_bool(node, "linux,pci-probe-only");
+}
+
 /**
  * devm_of_pci_get_host_bridge_resources() - Resource-managed parsing of PCI
  *                                           host bridge resources from DT
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 795534589b98..c57648084503 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -15,6 +15,7 @@
 #include <linux/cpumask.h>
 #include <linux/aer.h>
 #include <linux/acpi.h>
+#include <linux/pci-acpi.h>
 #include <linux/hypervisor.h>
 #include <linux/irqdomain.h>
 #include <linux/pm_runtime.h>
@@ -877,6 +878,28 @@ static void pci_set_bus_msi_domain(struct pci_bus *bus)
 	dev_set_msi_domain(&bus->dev, d);
 }
 
+static void pci_check_config_preserve(struct pci_host_bridge *host_bridge)
+{
+	if (ACPI_HANDLE(&host_bridge->dev)) {
+		union acpi_object *obj;
+
+		/*
+		 * Evaluate the "PCI Boot Configuration" _DSM Function.  If it
+		 * exists and returns 0, we must preserve any PCI resource
+		 * assignments made by firmware for this host bridge.
+		 */
+		obj = acpi_evaluate_dsm(ACPI_HANDLE(&host_bridge->dev), &pci_acpi_dsm_guid, 1,
+					DSM_PCI_PRESERVE_BOOT_CONFIG, NULL);
+		if (obj && obj->type == ACPI_TYPE_INTEGER && obj->integer.value == 0)
+			host_bridge->preserve_config = 1;
+		ACPI_FREE(obj);
+	}
+
+	if (host_bridge->dev.parent && host_bridge->dev.parent->of_node)
+		host_bridge->preserve_config =
+			of_pci_bridge_preserve_resources(host_bridge->dev.parent->of_node);
+}
+
 static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 {
 	struct device *parent = bridge->dev.parent;
@@ -971,6 +994,9 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 	if (nr_node_ids > 1 && pcibus_to_node(bus) == NUMA_NO_NODE)
 		dev_warn(&bus->dev, "Unknown NUMA node; performance will be reduced\n");
 
+	/* Check if the boot configuration by FW needs to be preserved */
+	pci_check_config_preserve(bridge);
+
 	/* Coalesce contiguous windows */
 	resource_list_for_each_entry_safe(window, n, &resources) {
 		if (list_is_last(&window->node, &resources))
@@ -3080,20 +3106,18 @@ int pci_host_probe(struct pci_host_bridge *bridge)
 
 	bus = bridge->bus;
 
+	/* If we must preserve the resource configuration, claim now */
+	if (pci_has_flag(PCI_PROBE_ONLY) || bridge->preserve_config)
+		pci_bus_claim_resources(bus);
+
 	/*
-	 * We insert PCI resources into the iomem_resource and
-	 * ioport_resource trees in either pci_bus_claim_resources()
-	 * or pci_bus_assign_resources().
+	 * Assign whatever was left unassigned. If we didn't claim above,
+	 * this will reassign everything.
 	 */
-	if (pci_has_flag(PCI_PROBE_ONLY)) {
-		pci_bus_claim_resources(bus);
-	} else {
-		pci_bus_size_bridges(bus);
-		pci_bus_assign_resources(bus);
+	pci_assign_unassigned_root_bus_resources(bus);
 
-		list_for_each_entry(child, &bus->children, node)
-			pcie_bus_configure_settings(child);
-	}
+	list_for_each_entry(child, &bus->children, node)
+		pcie_bus_configure_settings(child);
 
 	pci_bus_add_devices(bus);
 	return 0;
diff --git a/include/linux/of_pci.h b/include/linux/of_pci.h
index 29658c0ee71f..3f3909a5d55d 100644
--- a/include/linux/of_pci.h
+++ b/include/linux/of_pci.h
@@ -13,6 +13,7 @@ struct device_node *of_pci_find_child_device(struct device_node *parent,
 					     unsigned int devfn);
 int of_pci_get_devfn(struct device_node *np);
 void of_pci_check_probe_only(void);
+bool of_pci_bridge_preserve_resources(struct device_node *node);
 #else
 static inline struct device_node *of_pci_find_child_device(struct device_node *parent,
 					     unsigned int devfn)
@@ -26,6 +27,11 @@ static inline int of_pci_get_devfn(struct device_node *np)
 }
 
 static inline void of_pci_check_probe_only(void) { }
+
+static inline bool of_pci_bridge_preserve_resources(struct device_node *node)
+{
+	return false;
+}
 #endif
 
 #if IS_ENABLED(CONFIG_OF_IRQ)
-- 
2.25.1

Re: [PATCH V4] PCI: Add support for preserving boot configuration

[Rob Herring]

On Fri, Feb 23, 2024 at 01:30:21PM +0530, Vidya Sagar wrote:
> Add support for preserving the boot configuration done by the
> platform firmware per host bridge basis, based on the presence of
> 'linux,pci-probe-only' property in the respective PCI host bridge
> device-tree node. It also unifies the ACPI and DT based boot flows
> in this regard.
> 
> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> ---
> V4:
> * Addressed Bjorn's review comments
> 
> V3:
> * Unified ACPI and DT flows as part of addressing Bjorn's review comments
> 
> V2:
> * Addressed issues reported by kernel test robot <lkp@intel.com>
> 
>  drivers/acpi/pci_root.c                  | 12 -------
>  drivers/pci/controller/pci-host-common.c |  4 ---
>  drivers/pci/of.c                         | 21 +++++++++++
>  drivers/pci/probe.c                      | 46 ++++++++++++++++++------
>  include/linux/of_pci.h                   |  6 ++++
>  5 files changed, 62 insertions(+), 27 deletions(-)
> 
> diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> index 84030804a763..ddc2b3e89111 100644
> --- a/drivers/acpi/pci_root.c
> +++ b/drivers/acpi/pci_root.c
> @@ -1008,7 +1008,6 @@ struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
>  	int node = acpi_get_node(device->handle);
>  	struct pci_bus *bus;
>  	struct pci_host_bridge *host_bridge;
> -	union acpi_object *obj;
>  
>  	info->root = root;
>  	info->bridge = device;
> @@ -1050,17 +1049,6 @@ struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
>  	if (!(root->osc_ext_control_set & OSC_CXL_ERROR_REPORTING_CONTROL))
>  		host_bridge->native_cxl_error = 0;
>  
> -	/*
> -	 * Evaluate the "PCI Boot Configuration" _DSM Function.  If it
> -	 * exists and returns 0, we must preserve any PCI resource
> -	 * assignments made by firmware for this host bridge.
> -	 */
> -	obj = acpi_evaluate_dsm(ACPI_HANDLE(bus->bridge), &pci_acpi_dsm_guid, 1,
> -				DSM_PCI_PRESERVE_BOOT_CONFIG, NULL);
> -	if (obj && obj->type == ACPI_TYPE_INTEGER && obj->integer.value == 0)
> -		host_bridge->preserve_config = 1;
> -	ACPI_FREE(obj);
> -
>  	acpi_dev_power_up_children_with_adr(device);
>  
>  	pci_scan_child_bus(bus);
> diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
> index 6be3266cd7b5..e2602e38ae45 100644
> --- a/drivers/pci/controller/pci-host-common.c
> +++ b/drivers/pci/controller/pci-host-common.c
> @@ -73,10 +73,6 @@ int pci_host_common_probe(struct platform_device *pdev)
>  	if (IS_ERR(cfg))
>  		return PTR_ERR(cfg);
>  
> -	/* Do not reassign resources if probe only */
> -	if (!pci_has_flag(PCI_PROBE_ONLY))
> -		pci_add_flags(PCI_REASSIGN_ALL_BUS);
> -
>  	bridge->sysdata = cfg;
>  	bridge->ops = (struct pci_ops *)&ops->pci_ops;
>  	bridge->msi_domain = true;
> diff --git a/drivers/pci/of.c b/drivers/pci/of.c
> index 51e3dd0ea5ab..f0f1156040a5 100644
> --- a/drivers/pci/of.c
> +++ b/drivers/pci/of.c
> @@ -258,6 +258,27 @@ void of_pci_check_probe_only(void)
>  }
>  EXPORT_SYMBOL_GPL(of_pci_check_probe_only);
>  
> +/**
> + * of_pci_bridge_preserve_resources - Return true if the boot configuration
> + *                                    needs to be preserved
> + * @node: Device tree node with the domain information.
> + *
> + * This function looks for "linux,pci-probe-only" property for a given
> + * PCI controller's node and returns true if found. Having this property
> + * for a PCI controller ensures that the kernel doesn't reconfigure the
> + * BARs and bridge windows that are already done by the platform firmware.
> + * NOTE: The scope of "linux,pci-probe-only" defined within a PCI bridge device
> + *       is limited to the hierarchy under that particular bridge device. whereas
> + *       the scope of "linux,pci-probe-only" defined within chosen node is
> + *       system wide.
> + *
> + * Return: true if the property exists false otherwise.
> + */
> +bool of_pci_bridge_preserve_resources(struct device_node *node)
> +{
> +	return of_property_read_bool(node, "linux,pci-probe-only");

This is the wrong type. The existing "linux,pci-probe-only" is a u32 and 
non-zero value means probe-only. This would return true for 
'linux,pci-probe-only = <0>'.

Also, this should also check chosen. If you make this work accepting 
NULL for node, then of_pci_check_probe_only() can be re-implemented to 
use it.



Rob

Re: [PATCH V4] PCI: Add support for preserving boot configuration

[Rob Herring]

On Fri, Feb 23, 2024 at 01:30:21PM +0530, Vidya Sagar wrote:
> Add support for preserving the boot configuration done by the
> platform firmware per host bridge basis, based on the presence of
> 'linux,pci-probe-only' property in the respective PCI host bridge
> device-tree node. It also unifies the ACPI and DT based boot flows
> in this regard.
> 
> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> ---
> V4:
> * Addressed Bjorn's review comments
> 
> V3:
> * Unified ACPI and DT flows as part of addressing Bjorn's review comments
> 
> V2:
> * Addressed issues reported by kernel test robot <lkp@intel.com>
> 
>  drivers/acpi/pci_root.c                  | 12 -------
>  drivers/pci/controller/pci-host-common.c |  4 ---
>  drivers/pci/of.c                         | 21 +++++++++++
>  drivers/pci/probe.c                      | 46 ++++++++++++++++++------
>  include/linux/of_pci.h                   |  6 ++++
>  5 files changed, 62 insertions(+), 27 deletions(-)

One more thing.

> @@ -3080,20 +3106,18 @@ int pci_host_probe(struct pci_host_bridge *bridge)
>  
>  	bus = bridge->bus;
>  
> +	/* If we must preserve the resource configuration, claim now */
> +	if (pci_has_flag(PCI_PROBE_ONLY) || bridge->preserve_config)
> +		pci_bus_claim_resources(bus);

No reason to check PCI_PROBE_ONLY if you set preserve_config based on 
/chosen as well. IOW, we should deprecate PCI_PROBE_ONLY flag in favor 
of the per host bridge setting.

Rob

[PATCH V5] PCI: Add support for preserving boot configuration

[Vidya Sagar]

Add support for preserving the boot configuration done by the
platform firmware per host bridge basis, based on the presence of
'linux,pci-probe-only' property in the respective PCI host bridge
device-tree node. It also unifies the ACPI and DT based boot flows
in this regard.

Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
---
V5:
* Addressed Rob's review comments

V4:
* Addressed Bjorn's review comments

V3:
* Unified ACPI and DT flows as part of addressing Bjorn's review comments

V2:
* Addressed issues reported by kernel test robot <lkp@intel.com>

 drivers/acpi/pci_root.c                  | 12 -----
 drivers/pci/controller/pci-host-common.c |  4 --
 drivers/pci/of.c                         | 57 +++++++++++++++++++-----
 drivers/pci/probe.c                      | 46 ++++++++++++++-----
 include/linux/of_pci.h                   |  6 +++
 5 files changed, 88 insertions(+), 37 deletions(-)

diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
index 84030804a763..ddc2b3e89111 100644
--- a/drivers/acpi/pci_root.c
+++ b/drivers/acpi/pci_root.c
@@ -1008,7 +1008,6 @@ struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
 	int node = acpi_get_node(device->handle);
 	struct pci_bus *bus;
 	struct pci_host_bridge *host_bridge;
-	union acpi_object *obj;
 
 	info->root = root;
 	info->bridge = device;
@@ -1050,17 +1049,6 @@ struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
 	if (!(root->osc_ext_control_set & OSC_CXL_ERROR_REPORTING_CONTROL))
 		host_bridge->native_cxl_error = 0;
 
-	/*
-	 * Evaluate the "PCI Boot Configuration" _DSM Function.  If it
-	 * exists and returns 0, we must preserve any PCI resource
-	 * assignments made by firmware for this host bridge.
-	 */
-	obj = acpi_evaluate_dsm(ACPI_HANDLE(bus->bridge), &pci_acpi_dsm_guid, 1,
-				DSM_PCI_PRESERVE_BOOT_CONFIG, NULL);
-	if (obj && obj->type == ACPI_TYPE_INTEGER && obj->integer.value == 0)
-		host_bridge->preserve_config = 1;
-	ACPI_FREE(obj);
-
 	acpi_dev_power_up_children_with_adr(device);
 
 	pci_scan_child_bus(bus);
diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
index 6be3266cd7b5..e2602e38ae45 100644
--- a/drivers/pci/controller/pci-host-common.c
+++ b/drivers/pci/controller/pci-host-common.c
@@ -73,10 +73,6 @@ int pci_host_common_probe(struct platform_device *pdev)
 	if (IS_ERR(cfg))
 		return PTR_ERR(cfg);
 
-	/* Do not reassign resources if probe only */
-	if (!pci_has_flag(PCI_PROBE_ONLY))
-		pci_add_flags(PCI_REASSIGN_ALL_BUS);
-
 	bridge->sysdata = cfg;
 	bridge->ops = (struct pci_ops *)&ops->pci_ops;
 	bridge->msi_domain = true;
diff --git a/drivers/pci/of.c b/drivers/pci/of.c
index 51e3dd0ea5ab..e6da3654f9ac 100644
--- a/drivers/pci/of.c
+++ b/drivers/pci/of.c
@@ -239,24 +239,61 @@ EXPORT_SYMBOL_GPL(of_get_pci_domain_nr);
  */
 void of_pci_check_probe_only(void)
 {
-	u32 val;
+	bool is_preserve_config = of_pci_bridge_preserve_resources(of_chosen);
+
+	if (is_preserve_config)
+		pci_add_flags(PCI_PROBE_ONLY);
+	else
+		pci_clear_flags(PCI_PROBE_ONLY);
+
+	pr_info("PROBE_ONLY %s\n", is_preserve_config ? "enabled" : "disabled");
+}
+EXPORT_SYMBOL_GPL(of_pci_check_probe_only);
+
+/**
+ * of_pci_bridge_preserve_resources - Return true if the boot configuration
+ *                                    needs to be preserved
+ * @node: Device tree node.
+ *
+ * This function looks for "linux,pci-probe-only" property for a given
+ * PCI controller's node and returns true if found. It will also look in the
+ * chosen node if the property is not found in the given controller's node.
+ * Having this property ensures that the kernel doesn't reconfigure the
+ * BARs and bridge windows that are already done by the platform firmware.
+ *
+ * Return: true if the property exists false otherwise.
+ */
+bool of_pci_bridge_preserve_resources(struct device_node *node)
+{
+	u32 val = 0;
 	int ret;
 
-	ret = of_property_read_u32(of_chosen, "linux,pci-probe-only", &val);
+	if (!node) {
+		pr_warn("device node is NULL, trying with of_chosen\n");
+		node = of_chosen;
+	}
+
+retry:
+	ret = of_property_read_u32(node, "linux,pci-probe-only", &val);
 	if (ret) {
-		if (ret == -ENODATA || ret == -EOVERFLOW)
-			pr_warn("linux,pci-probe-only without valid value, ignoring\n");
-		return;
+		if (ret == -ENODATA || ret == -EOVERFLOW) {
+			pr_warn("Incorrect value for linux,pci-probe-only in %pOF, ignoring\n", node);
+			return false;
+		}
+		if (ret == -EINVAL) {
+			if (node == of_chosen)
+				return false;
+
+			node = of_chosen;
+			goto retry;
+		}
 	}
 
 	if (val)
-		pci_add_flags(PCI_PROBE_ONLY);
+		return true;
 	else
-		pci_clear_flags(PCI_PROBE_ONLY);
-
-	pr_info("PROBE_ONLY %s\n", val ? "enabled" : "disabled");
+		return false;
 }
-EXPORT_SYMBOL_GPL(of_pci_check_probe_only);
 
 /**
  * devm_of_pci_get_host_bridge_resources() - Resource-managed parsing of PCI
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 795534589b98..b0e0226a8da8 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -15,6 +15,7 @@
 #include <linux/cpumask.h>
 #include <linux/aer.h>
 #include <linux/acpi.h>
+#include <linux/pci-acpi.h>
 #include <linux/hypervisor.h>
 #include <linux/irqdomain.h>
 #include <linux/pm_runtime.h>
@@ -877,6 +878,28 @@ static void pci_set_bus_msi_domain(struct pci_bus *bus)
 	dev_set_msi_domain(&bus->dev, d);
 }
 
+static void pci_check_config_preserve(struct pci_host_bridge *host_bridge)
+{
+	if (ACPI_HANDLE(&host_bridge->dev)) {
+		union acpi_object *obj;
+
+		/*
+		 * Evaluate the "PCI Boot Configuration" _DSM Function.  If it
+		 * exists and returns 0, we must preserve any PCI resource
+		 * assignments made by firmware for this host bridge.
+		 */
+		obj = acpi_evaluate_dsm(ACPI_HANDLE(&host_bridge->dev), &pci_acpi_dsm_guid, 1,
+					DSM_PCI_PRESERVE_BOOT_CONFIG, NULL);
+		if (obj && obj->type == ACPI_TYPE_INTEGER && obj->integer.value == 0)
+			host_bridge->preserve_config = 1;
+		ACPI_FREE(obj);
+	}
+
+	if (host_bridge->dev.parent && host_bridge->dev.parent->of_node)
+		host_bridge->preserve_config =
+			of_pci_bridge_preserve_resources(host_bridge->dev.parent->of_node);
+}
+
 static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 {
 	struct device *parent = bridge->dev.parent;
@@ -971,6 +994,9 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 	if (nr_node_ids > 1 && pcibus_to_node(bus) == NUMA_NO_NODE)
 		dev_warn(&bus->dev, "Unknown NUMA node; performance will be reduced\n");
 
+	/* Check if the boot configuration by FW needs to be preserved */
+	pci_check_config_preserve(bridge);
+
 	/* Coalesce contiguous windows */
 	resource_list_for_each_entry_safe(window, n, &resources) {
 		if (list_is_last(&window->node, &resources))
@@ -3080,20 +3106,18 @@ int pci_host_probe(struct pci_host_bridge *bridge)
 
 	bus = bridge->bus;
 
+	/* If we must preserve the resource configuration, claim now */
+	if (bridge->preserve_config)
+		pci_bus_claim_resources(bus);
+
 	/*
-	 * We insert PCI resources into the iomem_resource and
-	 * ioport_resource trees in either pci_bus_claim_resources()
-	 * or pci_bus_assign_resources().
+	 * Assign whatever was left unassigned. If we didn't claim above,
+	 * this will reassign everything.
 	 */
-	if (pci_has_flag(PCI_PROBE_ONLY)) {
-		pci_bus_claim_resources(bus);
-	} else {
-		pci_bus_size_bridges(bus);
-		pci_bus_assign_resources(bus);
+	pci_assign_unassigned_root_bus_resources(bus);
 
-		list_for_each_entry(child, &bus->children, node)
-			pcie_bus_configure_settings(child);
-	}
+	list_for_each_entry(child, &bus->children, node)
+		pcie_bus_configure_settings(child);
 
 	pci_bus_add_devices(bus);
 	return 0;
diff --git a/include/linux/of_pci.h b/include/linux/of_pci.h
index 29658c0ee71f..3f3909a5d55d 100644
--- a/include/linux/of_pci.h
+++ b/include/linux/of_pci.h
@@ -13,6 +13,7 @@ struct device_node *of_pci_find_child_device(struct device_node *parent,
 					     unsigned int devfn);
 int of_pci_get_devfn(struct device_node *np);
 void of_pci_check_probe_only(void);
+bool of_pci_bridge_preserve_resources(struct device_node *node);
 #else
 static inline struct device_node *of_pci_find_child_device(struct device_node *parent,
 					     unsigned int devfn)
@@ -26,6 +27,11 @@ static inline int of_pci_get_devfn(struct device_node *np)
 }
 
 static inline void of_pci_check_probe_only(void) { }
+
+static inline bool of_pci_bridge_preserve_resources(struct device_node *node)
+{
+	return false;
+}
 #endif
 
 #if IS_ENABLED(CONFIG_OF_IRQ)
-- 
2.25.1

Re: [PATCH V5] PCI: Add support for preserving boot configuration

[Rob Herring]

On Mon, 01 Apr 2024 13:20:31 +0530, Vidya Sagar wrote:
> Add support for preserving the boot configuration done by the
> platform firmware per host bridge basis, based on the presence of
> 'linux,pci-probe-only' property in the respective PCI host bridge
> device-tree node. It also unifies the ACPI and DT based boot flows
> in this regard.
> 
> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> ---
> V5:
> * Addressed Rob's review comments
> 
> V4:
> * Addressed Bjorn's review comments
> 
> V3:
> * Unified ACPI and DT flows as part of addressing Bjorn's review comments
> 
> V2:
> * Addressed issues reported by kernel test robot <lkp@intel.com>
> 
>  drivers/acpi/pci_root.c                  | 12 -----
>  drivers/pci/controller/pci-host-common.c |  4 --
>  drivers/pci/of.c                         | 57 +++++++++++++++++++-----
>  drivers/pci/probe.c                      | 46 ++++++++++++++-----
>  include/linux/of_pci.h                   |  6 +++
>  5 files changed, 88 insertions(+), 37 deletions(-)
> 

Reviewed-by: Rob Herring <robh@kernel.org>

Re: [PATCH V5] PCI: Add support for preserving boot configuration

[Vidya Sagar]

Thanks Rob for the review.
Bjorn, do you have any further comments for this patch?

On 02-04-2024 21:31, Rob Herring wrote:
> External email: Use caution opening links or attachments
>
>
> On Mon, 01 Apr 2024 13:20:31 +0530, Vidya Sagar wrote:
>> Add support for preserving the boot configuration done by the
>> platform firmware per host bridge basis, based on the presence of
>> 'linux,pci-probe-only' property in the respective PCI host bridge
>> device-tree node. It also unifies the ACPI and DT based boot flows
>> in this regard.
>>
>> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
>> ---
>> V5:
>> * Addressed Rob's review comments
>>
>> V4:
>> * Addressed Bjorn's review comments
>>
>> V3:
>> * Unified ACPI and DT flows as part of addressing Bjorn's review comments
>>
>> V2:
>> * Addressed issues reported by kernel test robot <lkp@intel.com>
>>
>>   drivers/acpi/pci_root.c                  | 12 -----
>>   drivers/pci/controller/pci-host-common.c |  4 --
>>   drivers/pci/of.c                         | 57 +++++++++++++++++++-----
>>   drivers/pci/probe.c                      | 46 ++++++++++++++-----
>>   include/linux/of_pci.h                   |  6 +++
>>   5 files changed, 88 insertions(+), 37 deletions(-)
>>
> Reviewed-by: Rob Herring <robh@kernel.org>
>

Re: [PATCH V5] PCI: Add support for preserving boot configuration

[Bjorn Helgaas]

On Mon, Apr 01, 2024 at 01:20:31PM +0530, Vidya Sagar wrote:
> Add support for preserving the boot configuration done by the
> platform firmware per host bridge basis, based on the presence of
> 'linux,pci-probe-only' property in the respective PCI host bridge
> device-tree node. It also unifies the ACPI and DT based boot flows
> in this regard.

>  drivers/acpi/pci_root.c                  | 12 -----
>  drivers/pci/controller/pci-host-common.c |  4 --
>  drivers/pci/of.c                         | 57 +++++++++++++++++++-----
>  drivers/pci/probe.c                      | 46 ++++++++++++++-----
>  include/linux/of_pci.h                   |  6 +++
>  5 files changed, 88 insertions(+), 37 deletions(-)

What does this apply to?  I tried v6.9-rc1:

  $ git checkout -b wip/2404-vidya-preserve-boot-v5 v6.9-rc1
  Switched to a new branch 'wip/2404-vidya-preserve-boot-v5'

  $ git am m/v5_20240401_vidyas_pci_add_support_for_preserving_boot_configuration.mbx
  Applying: PCI: Add support for preserving boot configuration
  error: patch failed: drivers/acpi/pci_root.c:1050
  error: drivers/acpi/pci_root.c: patch does not apply
  Patch failed at 0001 PCI: Add support for preserving boot configuration

> diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> index 84030804a763..ddc2b3e89111 100644
> --- a/drivers/acpi/pci_root.c
> +++ b/drivers/acpi/pci_root.c
> @@ -1008,7 +1008,6 @@ struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
>  	int node = acpi_get_node(device->handle);
>  	struct pci_bus *bus;
>  	struct pci_host_bridge *host_bridge;
> -	union acpi_object *obj;
>  
>  	info->root = root;
>  	info->bridge = device;
> @@ -1050,17 +1049,6 @@ struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
>  	if (!(root->osc_ext_control_set & OSC_CXL_ERROR_REPORTING_CONTROL))
>  		host_bridge->native_cxl_error = 0;
>  
> -	/*
> -	 * Evaluate the "PCI Boot Configuration" _DSM Function.  If it
> -	 * exists and returns 0, we must preserve any PCI resource
> -	 * assignments made by firmware for this host bridge.
> -	 */
> -	obj = acpi_evaluate_dsm(ACPI_HANDLE(bus->bridge), &pci_acpi_dsm_guid, 1,
> -				DSM_PCI_PRESERVE_BOOT_CONFIG, NULL);
> -	if (obj && obj->type == ACPI_TYPE_INTEGER && obj->integer.value == 0)
> -		host_bridge->preserve_config = 1;
> -	ACPI_FREE(obj);
> -
>  	acpi_dev_power_up_children_with_adr(device);
>  
>  	pci_scan_child_bus(bus);
> diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
> index 6be3266cd7b5..e2602e38ae45 100644
> --- a/drivers/pci/controller/pci-host-common.c
> +++ b/drivers/pci/controller/pci-host-common.c
> @@ -73,10 +73,6 @@ int pci_host_common_probe(struct platform_device *pdev)
>  	if (IS_ERR(cfg))
>  		return PTR_ERR(cfg);
>  
> -	/* Do not reassign resources if probe only */
> -	if (!pci_has_flag(PCI_PROBE_ONLY))
> -		pci_add_flags(PCI_REASSIGN_ALL_BUS);
> -
>  	bridge->sysdata = cfg;
>  	bridge->ops = (struct pci_ops *)&ops->pci_ops;
>  	bridge->msi_domain = true;
> diff --git a/drivers/pci/of.c b/drivers/pci/of.c
> index 51e3dd0ea5ab..e6da3654f9ac 100644
> --- a/drivers/pci/of.c
> +++ b/drivers/pci/of.c
> @@ -239,24 +239,61 @@ EXPORT_SYMBOL_GPL(of_get_pci_domain_nr);
>   */
>  void of_pci_check_probe_only(void)
>  {
> -	u32 val;
> +	bool is_preserve_config = of_pci_bridge_preserve_resources(of_chosen);

No need for a bool here:

  if (of_pci_bridge_preserve_resources(of_chosen))
    pci_add_flags(PCI_PROBE_ONLY);

I think it would make more sense to add
of_pci_bridge_preserve_resources() *above* of_pci_check_probe_only()
since the usual order is to define functions earlier in the file than
the calls.

> +
> +	if (is_preserve_config)
> +		pci_add_flags(PCI_PROBE_ONLY);
> +	else
> +		pci_clear_flags(PCI_PROBE_ONLY);

Not related to *this* patch, but I see that of_pci_check_probe_only()
already clears PCI_PROBE_ONLY (added by f81c11af617c ("of/pci: Add
of_pci_check_probe_only to parse "linux,pci-probe-only"").

I'm concerned about clearing PCI_PROBE_ONLY because some platforms set
this unconditionally, and I don't think they necessarily have
"linux,pci-probe-only" in DT.

Apparently none of them currently calls of_pci_check_probe_only() so
PCI_PROBE_ONLY remains set, but clearing it here feels like a landmine
waiting for somebody to move this into a unified call path.

I guess if we were to drop pci_clear_flags(), that should be a
separate patch in case it breaks something.

> +	pr_info("PROBE_ONLY %s\n", is_preserve_config ? "enabled" : "disabled");
> +}
> +EXPORT_SYMBOL_GPL(of_pci_check_probe_only);
> +
> +/**
> + * of_pci_bridge_preserve_resources - Return true if the boot configuration
> + *                                    needs to be preserved
> + * @node: Device tree node.
> + *
> + * This function looks for "linux,pci-probe-only" property for a given
> + * PCI controller's node and returns true if found. It will also look in the
> + * chosen node if the property is not found in the given controller's node.
> + * Having this property ensures that the kernel doesn't reconfigure the
> + * BARs and bridge windows that are already done by the platform firmware.
> + *
> + * Return: true if the property exists false otherwise.
> + */
> +bool of_pci_bridge_preserve_resources(struct device_node *node)
> +{
> +	u32 val = 0;
>  	int ret;
>  
> -	ret = of_property_read_u32(of_chosen, "linux,pci-probe-only", &val);
> +	if (!node) {
> +		pr_warn("device node is NULL, trying with of_chosen\n");
> +		node = of_chosen;
> +	}
> +
> +retry:
> +	ret = of_property_read_u32(node, "linux,pci-probe-only", &val);
>  	if (ret) {
> -		if (ret == -ENODATA || ret == -EOVERFLOW)
> -			pr_warn("linux,pci-probe-only without valid value, ignoring\n");
> -		return;
> +		if (ret == -ENODATA || ret == -EOVERFLOW) {
> +			pr_warn("Incorrect value for linux,pci-probe-only in %pOF, ignoring\n", node);
> +			return false;
> +		}
> +		if (ret == -EINVAL) {
> +			if (node == of_chosen)
> +				return false;
> +
> +			node = of_chosen;
> +			goto retry;
> +		}
>  	}
>  
>  	if (val)
> -		pci_add_flags(PCI_PROBE_ONLY);
> +		return true;
>  	else
> -		pci_clear_flags(PCI_PROBE_ONLY);
> -
> -	pr_info("PROBE_ONLY %s\n", val ? "enabled" : "disabled");
> +		return false;
>  }
> -EXPORT_SYMBOL_GPL(of_pci_check_probe_only);
>  
>  /**
>   * devm_of_pci_get_host_bridge_resources() - Resource-managed parsing of PCI
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 795534589b98..b0e0226a8da8 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -15,6 +15,7 @@
>  #include <linux/cpumask.h>
>  #include <linux/aer.h>
>  #include <linux/acpi.h>
> +#include <linux/pci-acpi.h>
>  #include <linux/hypervisor.h>
>  #include <linux/irqdomain.h>
>  #include <linux/pm_runtime.h>
> @@ -877,6 +878,28 @@ static void pci_set_bus_msi_domain(struct pci_bus *bus)
>  	dev_set_msi_domain(&bus->dev, d);
>  }
>  
> +static void pci_check_config_preserve(struct pci_host_bridge *host_bridge)
> +{
> +	if (ACPI_HANDLE(&host_bridge->dev)) {
> +		union acpi_object *obj;
> +
> +		/*
> +		 * Evaluate the "PCI Boot Configuration" _DSM Function.  If it
> +		 * exists and returns 0, we must preserve any PCI resource
> +		 * assignments made by firmware for this host bridge.
> +		 */
> +		obj = acpi_evaluate_dsm(ACPI_HANDLE(&host_bridge->dev), &pci_acpi_dsm_guid, 1,
> +					DSM_PCI_PRESERVE_BOOT_CONFIG, NULL);
> +		if (obj && obj->type == ACPI_TYPE_INTEGER && obj->integer.value == 0)
> +			host_bridge->preserve_config = 1;
> +		ACPI_FREE(obj);
> +	}
> +
> +	if (host_bridge->dev.parent && host_bridge->dev.parent->of_node)
> +		host_bridge->preserve_config =
> +			of_pci_bridge_preserve_resources(host_bridge->dev.parent->of_node);
> +}
> +
>  static int pci_register_host_bridge(struct pci_host_bridge *bridge)
>  {
>  	struct device *parent = bridge->dev.parent;
> @@ -971,6 +994,9 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
>  	if (nr_node_ids > 1 && pcibus_to_node(bus) == NUMA_NO_NODE)
>  		dev_warn(&bus->dev, "Unknown NUMA node; performance will be reduced\n");
>  
> +	/* Check if the boot configuration by FW needs to be preserved */
> +	pci_check_config_preserve(bridge);

I really have an allergic reaction to functions named "..._check_..."
We can tell that the function has something to do with preserving
configuration, and it's void so obviously the side effects are the
important thing, but there's no clue in the caller about what the side
effects are.

I'd prefer something like:

  bridge->preserve_config = pci_must_preserve_config(bridge);

where pci_must_preserve_config() has no side effects, returns bool,
and the action is at the caller.

>  	/* Coalesce contiguous windows */
>  	resource_list_for_each_entry_safe(window, n, &resources) {
>  		if (list_is_last(&window->node, &resources))
> @@ -3080,20 +3106,18 @@ int pci_host_probe(struct pci_host_bridge *bridge)
>  
>  	bus = bridge->bus;
>  
> +	/* If we must preserve the resource configuration, claim now */
> +	if (bridge->preserve_config)
> +		pci_bus_claim_resources(bus);
> +
>  	/*
> -	 * We insert PCI resources into the iomem_resource and
> -	 * ioport_resource trees in either pci_bus_claim_resources()
> -	 * or pci_bus_assign_resources().
> +	 * Assign whatever was left unassigned. If we didn't claim above,
> +	 * this will reassign everything.
>  	 */
> -	if (pci_has_flag(PCI_PROBE_ONLY)) {
> -		pci_bus_claim_resources(bus);
> -	} else {
> -		pci_bus_size_bridges(bus);
> -		pci_bus_assign_resources(bus);
> +	pci_assign_unassigned_root_bus_resources(bus);
>  
> -		list_for_each_entry(child, &bus->children, node)
> -			pcie_bus_configure_settings(child);
> -	}
> +	list_for_each_entry(child, &bus->children, node)
> +		pcie_bus_configure_settings(child);
>  
>  	pci_bus_add_devices(bus);
>  	return 0;
> diff --git a/include/linux/of_pci.h b/include/linux/of_pci.h
> index 29658c0ee71f..3f3909a5d55d 100644
> --- a/include/linux/of_pci.h
> +++ b/include/linux/of_pci.h
> @@ -13,6 +13,7 @@ struct device_node *of_pci_find_child_device(struct device_node *parent,
>  					     unsigned int devfn);
>  int of_pci_get_devfn(struct device_node *np);
>  void of_pci_check_probe_only(void);
> +bool of_pci_bridge_preserve_resources(struct device_node *node);

This looks like it should be in drivers/pci/pci.h since it's not used
outside drivers/pci/.

>  #else
>  static inline struct device_node *of_pci_find_child_device(struct device_node *parent,
>  					     unsigned int devfn)
> @@ -26,6 +27,11 @@ static inline int of_pci_get_devfn(struct device_node *np)
>  }
>  
>  static inline void of_pci_check_probe_only(void) { }
> +
> +static inline bool of_pci_bridge_preserve_resources(struct device_node *node)
> +{
> +	return false;
> +}
>  #endif
>  
>  #if IS_ENABLED(CONFIG_OF_IRQ)
> -- 
> 2.25.1
> 

Re: [PATCH V5] PCI: Add support for preserving boot configuration

[Vidya Sagar]

Replied inline...

On 11-04-2024 02:20, Bjorn Helgaas wrote:
> External email: Use caution opening links or attachments
>
>
> On Mon, Apr 01, 2024 at 01:20:31PM +0530, Vidya Sagar wrote:
>> Add support for preserving the boot configuration done by the
>> platform firmware per host bridge basis, based on the presence of
>> 'linux,pci-probe-only' property in the respective PCI host bridge
>> device-tree node. It also unifies the ACPI and DT based boot flows
>> in this regard.
>>   drivers/acpi/pci_root.c                  | 12 -----
>>   drivers/pci/controller/pci-host-common.c |  4 --
>>   drivers/pci/of.c                         | 57 +++++++++++++++++++-----
>>   drivers/pci/probe.c                      | 46 ++++++++++++++-----
>>   include/linux/of_pci.h                   |  6 +++
>>   5 files changed, 88 insertions(+), 37 deletions(-)
> What does this apply to?  I tried v6.9-rc1:
>
>    $ git checkout -b wip/2404-vidya-preserve-boot-v5 v6.9-rc1
>    Switched to a new branch 'wip/2404-vidya-preserve-boot-v5'
>
>    $ git am m/v5_20240401_vidyas_pci_add_support_for_preserving_boot_configuration.mbx
>    Applying: PCI: Add support for preserving boot configuration
>    error: patch failed: drivers/acpi/pci_root.c:1050
>    error: drivers/acpi/pci_root.c: patch does not apply
>    Patch failed at 0001 PCI: Add support for preserving boot configuration
I'm going to rebase this patch on top of linux-next and send.
>> diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
>> index 84030804a763..ddc2b3e89111 100644
>> --- a/drivers/acpi/pci_root.c
>> +++ b/drivers/acpi/pci_root.c
>> @@ -1008,7 +1008,6 @@ struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
>>        int node = acpi_get_node(device->handle);
>>        struct pci_bus *bus;
>>        struct pci_host_bridge *host_bridge;
>> -     union acpi_object *obj;
>>
>>        info->root = root;
>>        info->bridge = device;
>> @@ -1050,17 +1049,6 @@ struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
>>        if (!(root->osc_ext_control_set & OSC_CXL_ERROR_REPORTING_CONTROL))
>>                host_bridge->native_cxl_error = 0;
>>
>> -     /*
>> -      * Evaluate the "PCI Boot Configuration" _DSM Function.  If it
>> -      * exists and returns 0, we must preserve any PCI resource
>> -      * assignments made by firmware for this host bridge.
>> -      */
>> -     obj = acpi_evaluate_dsm(ACPI_HANDLE(bus->bridge), &pci_acpi_dsm_guid, 1,
>> -                             DSM_PCI_PRESERVE_BOOT_CONFIG, NULL);
>> -     if (obj && obj->type == ACPI_TYPE_INTEGER && obj->integer.value == 0)
>> -             host_bridge->preserve_config = 1;
>> -     ACPI_FREE(obj);
>> -
>>        acpi_dev_power_up_children_with_adr(device);
>>
>>        pci_scan_child_bus(bus);
>> diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
>> index 6be3266cd7b5..e2602e38ae45 100644
>> --- a/drivers/pci/controller/pci-host-common.c
>> +++ b/drivers/pci/controller/pci-host-common.c
>> @@ -73,10 +73,6 @@ int pci_host_common_probe(struct platform_device *pdev)
>>        if (IS_ERR(cfg))
>>                return PTR_ERR(cfg);
>>
>> -     /* Do not reassign resources if probe only */
>> -     if (!pci_has_flag(PCI_PROBE_ONLY))
>> -             pci_add_flags(PCI_REASSIGN_ALL_BUS);
>> -
>>        bridge->sysdata = cfg;
>>        bridge->ops = (struct pci_ops *)&ops->pci_ops;
>>        bridge->msi_domain = true;
>> diff --git a/drivers/pci/of.c b/drivers/pci/of.c
>> index 51e3dd0ea5ab..e6da3654f9ac 100644
>> --- a/drivers/pci/of.c
>> +++ b/drivers/pci/of.c
>> @@ -239,24 +239,61 @@ EXPORT_SYMBOL_GPL(of_get_pci_domain_nr);
>>    */
>>   void of_pci_check_probe_only(void)
>>   {
>> -     u32 val;
>> +     bool is_preserve_config = of_pci_bridge_preserve_resources(of_chosen);
> No need for a bool here:
>
>    if (of_pci_bridge_preserve_resources(of_chosen))
>      pci_add_flags(PCI_PROBE_ONLY);
>
> I think it would make more sense to add
> of_pci_bridge_preserve_resources() *above* of_pci_check_probe_only()
> since the usual order is to define functions earlier in the file than
> the calls.
I'll take care of it in the next patch.
>> +
>> +     if (is_preserve_config)
>> +             pci_add_flags(PCI_PROBE_ONLY);
>> +     else
>> +             pci_clear_flags(PCI_PROBE_ONLY);
> Not related to *this* patch, but I see that of_pci_check_probe_only()
> already clears PCI_PROBE_ONLY (added by f81c11af617c ("of/pci: Add
> of_pci_check_probe_only to parse "linux,pci-probe-only"").
>
> I'm concerned about clearing PCI_PROBE_ONLY because some platforms set
> this unconditionally, and I don't think they necessarily have
> "linux,pci-probe-only" in DT.
>
> Apparently none of them currently calls of_pci_check_probe_only() so
> PCI_PROBE_ONLY remains set, but clearing it here feels like a landmine
> waiting for somebody to move this into a unified call path.
>
> I guess if we were to drop pci_clear_flags(), that should be a
> separate patch in case it breaks something.
As far as the current patch is concerned, since it is not going to do anything
different compared to what already exists, I'll leave it at it for now and
ponder over moving pci_clear_flags() to a different patch later.
>
>> +     pr_info("PROBE_ONLY %s\n", is_preserve_config ? "enabled" : "disabled");
>> +}
>> +EXPORT_SYMBOL_GPL(of_pci_check_probe_only);
>> +
>> +/**
>> + * of_pci_bridge_preserve_resources - Return true if the boot configuration
>> + *                                    needs to be preserved
>> + * @node: Device tree node.
>> + *
>> + * This function looks for "linux,pci-probe-only" property for a given
>> + * PCI controller's node and returns true if found. It will also look in the
>> + * chosen node if the property is not found in the given controller's node.
>> + * Having this property ensures that the kernel doesn't reconfigure the
>> + * BARs and bridge windows that are already done by the platform firmware.
>> + *
>> + * Return: true if the property exists false otherwise.
>> + */
>> +bool of_pci_bridge_preserve_resources(struct device_node *node)
>> +{
>> +     u32 val = 0;
>>        int ret;
>>
>> -     ret = of_property_read_u32(of_chosen, "linux,pci-probe-only", &val);
>> +     if (!node) {
>> +             pr_warn("device node is NULL, trying with of_chosen\n");
>> +             node = of_chosen;
>> +     }
>> +
>> +retry:
>> +     ret = of_property_read_u32(node, "linux,pci-probe-only", &val);
>>        if (ret) {
>> -             if (ret == -ENODATA || ret == -EOVERFLOW)
>> -                     pr_warn("linux,pci-probe-only without valid value, ignoring\n");
>> -             return;
>> +             if (ret == -ENODATA || ret == -EOVERFLOW) {
>> +                     pr_warn("Incorrect value for linux,pci-probe-only in %pOF, ignoring\n", node);
>> +                     return false;
>> +             }
>> +             if (ret == -EINVAL) {
>> +                     if (node == of_chosen)
>> +                             return false;
>> +
>> +                     node = of_chosen;
>> +                     goto retry;
>> +             }
>>        }
>>
>>        if (val)
>> -             pci_add_flags(PCI_PROBE_ONLY);
>> +             return true;
>>        else
>> -             pci_clear_flags(PCI_PROBE_ONLY);
>> -
>> -     pr_info("PROBE_ONLY %s\n", val ? "enabled" : "disabled");
>> +             return false;
>>   }
>> -EXPORT_SYMBOL_GPL(of_pci_check_probe_only);
>>
>>   /**
>>    * devm_of_pci_get_host_bridge_resources() - Resource-managed parsing of PCI
>> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
>> index 795534589b98..b0e0226a8da8 100644
>> --- a/drivers/pci/probe.c
>> +++ b/drivers/pci/probe.c
>> @@ -15,6 +15,7 @@
>>   #include <linux/cpumask.h>
>>   #include <linux/aer.h>
>>   #include <linux/acpi.h>
>> +#include <linux/pci-acpi.h>
>>   #include <linux/hypervisor.h>
>>   #include <linux/irqdomain.h>
>>   #include <linux/pm_runtime.h>
>> @@ -877,6 +878,28 @@ static void pci_set_bus_msi_domain(struct pci_bus *bus)
>>        dev_set_msi_domain(&bus->dev, d);
>>   }
>>
>> +static void pci_check_config_preserve(struct pci_host_bridge *host_bridge)
>> +{
>> +     if (ACPI_HANDLE(&host_bridge->dev)) {
>> +             union acpi_object *obj;
>> +
>> +             /*
>> +              * Evaluate the "PCI Boot Configuration" _DSM Function.  If it
>> +              * exists and returns 0, we must preserve any PCI resource
>> +              * assignments made by firmware for this host bridge.
>> +              */
>> +             obj = acpi_evaluate_dsm(ACPI_HANDLE(&host_bridge->dev), &pci_acpi_dsm_guid, 1,
>> +                                     DSM_PCI_PRESERVE_BOOT_CONFIG, NULL);
>> +             if (obj && obj->type == ACPI_TYPE_INTEGER && obj->integer.value == 0)
>> +                     host_bridge->preserve_config = 1;
>> +             ACPI_FREE(obj);
>> +     }
>> +
>> +     if (host_bridge->dev.parent && host_bridge->dev.parent->of_node)
>> +             host_bridge->preserve_config =
>> +                     of_pci_bridge_preserve_resources(host_bridge->dev.parent->of_node);
>> +}
>> +
>>   static int pci_register_host_bridge(struct pci_host_bridge *bridge)
>>   {
>>        struct device *parent = bridge->dev.parent;
>> @@ -971,6 +994,9 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
>>        if (nr_node_ids > 1 && pcibus_to_node(bus) == NUMA_NO_NODE)
>>                dev_warn(&bus->dev, "Unknown NUMA node; performance will be reduced\n");
>>
>> +     /* Check if the boot configuration by FW needs to be preserved */
>> +     pci_check_config_preserve(bridge);
> I really have an allergic reaction to functions named "..._check_..."
> We can tell that the function has something to do with preserving
> configuration, and it's void so obviously the side effects are the
> important thing, but there's no clue in the caller about what the side
> effects are.
>
> I'd prefer something like:
>
>    bridge->preserve_config = pci_must_preserve_config(bridge);
>
> where pci_must_preserve_config() has no side effects, returns bool,
> and the action is at the caller.
I'll take care of it in the next patch.
>>        /* Coalesce contiguous windows */
>>        resource_list_for_each_entry_safe(window, n, &resources) {
>>                if (list_is_last(&window->node, &resources))
>> @@ -3080,20 +3106,18 @@ int pci_host_probe(struct pci_host_bridge *bridge)
>>
>>        bus = bridge->bus;
>>
>> +     /* If we must preserve the resource configuration, claim now */
>> +     if (bridge->preserve_config)
>> +             pci_bus_claim_resources(bus);
>> +
>>        /*
>> -      * We insert PCI resources into the iomem_resource and
>> -      * ioport_resource trees in either pci_bus_claim_resources()
>> -      * or pci_bus_assign_resources().
>> +      * Assign whatever was left unassigned. If we didn't claim above,
>> +      * this will reassign everything.
>>         */
>> -     if (pci_has_flag(PCI_PROBE_ONLY)) {
>> -             pci_bus_claim_resources(bus);
>> -     } else {
>> -             pci_bus_size_bridges(bus);
>> -             pci_bus_assign_resources(bus);
>> +     pci_assign_unassigned_root_bus_resources(bus);
>>
>> -             list_for_each_entry(child, &bus->children, node)
>> -                     pcie_bus_configure_settings(child);
>> -     }
>> +     list_for_each_entry(child, &bus->children, node)
>> +             pcie_bus_configure_settings(child);
>>
>>        pci_bus_add_devices(bus);
>>        return 0;
>> diff --git a/include/linux/of_pci.h b/include/linux/of_pci.h
>> index 29658c0ee71f..3f3909a5d55d 100644
>> --- a/include/linux/of_pci.h
>> +++ b/include/linux/of_pci.h
>> @@ -13,6 +13,7 @@ struct device_node *of_pci_find_child_device(struct device_node *parent,
>>                                             unsigned int devfn);
>>   int of_pci_get_devfn(struct device_node *np);
>>   void of_pci_check_probe_only(void);
>> +bool of_pci_bridge_preserve_resources(struct device_node *node);
> This looks like it should be in drivers/pci/pci.h since it's not used
> outside drivers/pci/.
Agree. I'll take care of it in the next patch.
>>   #else
>>   static inline struct device_node *of_pci_find_child_device(struct device_node *parent,
>>                                             unsigned int devfn)
>> @@ -26,6 +27,11 @@ static inline int of_pci_get_devfn(struct device_node *np)
>>   }
>>
>>   static inline void of_pci_check_probe_only(void) { }
>> +
>> +static inline bool of_pci_bridge_preserve_resources(struct device_node *node)
>> +{
>> +     return false;
>> +}
>>   #endif
>>
>>   #if IS_ENABLED(CONFIG_OF_IRQ)
>> --
>> 2.25.1
>>

[PATCH V6] PCI: Add support for preserving boot configuration

[Vidya Sagar]

Add support for preserving the boot configuration done by the
platform firmware per host bridge basis, based on the presence of
'linux,pci-probe-only' property in the respective PCI host bridge
device-tree node. It also unifies the ACPI and DT based boot flows
in this regard.

Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
---
V5:
* Addressed Rob's review comments

V4:
* Addressed Bjorn's review comments

V3:
* Unified ACPI and DT flows as part of addressing Bjorn's review comments

V2:
* Addressed issues reported by kernel test robot <lkp@intel.com>

 drivers/acpi/pci_root.c                  | 12 ------
 drivers/pci/controller/pci-host-common.c |  4 --
 drivers/pci/of.c                         | 54 +++++++++++++++++++-----
 drivers/pci/pci.h                        |  7 +++
 drivers/pci/probe.c                      | 48 ++++++++++++++++-----
 5 files changed, 88 insertions(+), 37 deletions(-)

diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
index 58b89b8d950e..ddc2b3e89111 100644
--- a/drivers/acpi/pci_root.c
+++ b/drivers/acpi/pci_root.c
@@ -1008,7 +1008,6 @@ struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
 	int node = acpi_get_node(device->handle);
 	struct pci_bus *bus;
 	struct pci_host_bridge *host_bridge;
-	union acpi_object *obj;
 
 	info->root = root;
 	info->bridge = device;
@@ -1050,17 +1049,6 @@ struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
 	if (!(root->osc_ext_control_set & OSC_CXL_ERROR_REPORTING_CONTROL))
 		host_bridge->native_cxl_error = 0;
 
-	/*
-	 * Evaluate the "PCI Boot Configuration" _DSM Function.  If it
-	 * exists and returns 0, we must preserve any PCI resource
-	 * assignments made by firmware for this host bridge.
-	 */
-	obj = acpi_evaluate_dsm_typed(ACPI_HANDLE(bus->bridge), &pci_acpi_dsm_guid, 1,
-				      DSM_PCI_PRESERVE_BOOT_CONFIG, NULL, ACPI_TYPE_INTEGER);
-	if (obj && obj->integer.value == 0)
-		host_bridge->preserve_config = 1;
-	ACPI_FREE(obj);
-
 	acpi_dev_power_up_children_with_adr(device);
 
 	pci_scan_child_bus(bus);
diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
index 45b71806182d..c96b2de163b5 100644
--- a/drivers/pci/controller/pci-host-common.c
+++ b/drivers/pci/controller/pci-host-common.c
@@ -73,10 +73,6 @@ int pci_host_common_probe(struct platform_device *pdev)
 	if (IS_ERR(cfg))
 		return PTR_ERR(cfg);
 
-	/* Do not reassign resources if probe only */
-	if (!pci_has_flag(PCI_PROBE_ONLY))
-		pci_add_flags(PCI_REASSIGN_ALL_BUS);
-
 	bridge->sysdata = cfg;
 	bridge->ops = (struct pci_ops *)&ops->pci_ops;
 	bridge->msi_domain = true;
diff --git a/drivers/pci/of.c b/drivers/pci/of.c
index 51e3dd0ea5ab..aeacff742706 100644
--- a/drivers/pci/of.c
+++ b/drivers/pci/of.c
@@ -234,27 +234,61 @@ int of_get_pci_domain_nr(struct device_node *node)
 EXPORT_SYMBOL_GPL(of_get_pci_domain_nr);
 
 /**
- * of_pci_check_probe_only - Setup probe only mode if linux,pci-probe-only
- *                           is present and valid
+ * of_pci_bridge_preserve_resources - Return true if the boot configuration
+ *                                    needs to be preserved
+ * @node: Device tree node.
+ *
+ * This function looks for "linux,pci-probe-only" property for a given
+ * PCI controller's node and returns true if found. It will also look in the
+ * chosen node if the property is not found in the given controller's node.
+ * Having this property ensures that the kernel doesn't reconfigure the
+ * BARs and bridge windows that are already done by the platform firmware.
+ *
+ * Return: true if the property exists false otherwise.
  */
-void of_pci_check_probe_only(void)
+bool of_pci_bridge_preserve_resources(struct device_node *node)
 {
-	u32 val;
+	u32 val = 0;
 	int ret;
 
-	ret = of_property_read_u32(of_chosen, "linux,pci-probe-only", &val);
+	if (!node) {
+		pr_warn("device node is NULL, trying with of_chosen\n");
+		node = of_chosen;
+	}
+
+retry:
+	ret = of_property_read_u32(node, "linux,pci-probe-only", &val);
 	if (ret) {
-		if (ret == -ENODATA || ret == -EOVERFLOW)
-			pr_warn("linux,pci-probe-only without valid value, ignoring\n");
-		return;
+		if (ret == -ENODATA || ret == -EOVERFLOW) {
+			pr_warn("Incorrect value for linux,pci-probe-only in %pOF, ignoring\n",
+				node);
+			return false;
+		}
+		if (ret == -EINVAL) {
+			if (node == of_chosen)
+				return false;
+
+			node = of_chosen;
+			goto retry;
+		}
 	}
 
 	if (val)
+		return true;
+	else
+		return false;
+}
+
+/**
+ * of_pci_check_probe_only - Setup probe only mode if linux,pci-probe-only
+ *                           is present and valid
+ */
+void of_pci_check_probe_only(void)
+{
+	if (of_pci_bridge_preserve_resources(of_chosen))
 		pci_add_flags(PCI_PROBE_ONLY);
 	else
 		pci_clear_flags(PCI_PROBE_ONLY);
-
-	pr_info("PROBE_ONLY %s\n", val ? "enabled" : "disabled");
 }
 EXPORT_SYMBOL_GPL(of_pci_check_probe_only);
 
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 17fed1846847..1da54ab18534 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -650,6 +650,7 @@ int of_pci_get_max_link_speed(struct device_node *node);
 u32 of_pci_get_slot_power_limit(struct device_node *node,
 				u8 *slot_power_limit_value,
 				u8 *slot_power_limit_scale);
+bool of_pci_bridge_preserve_resources(struct device_node *node);
 int pci_set_of_node(struct pci_dev *dev);
 void pci_release_of_node(struct pci_dev *dev);
 void pci_set_bus_of_node(struct pci_bus *bus);
@@ -688,6 +689,12 @@ of_pci_get_slot_power_limit(struct device_node *node,
 	return 0;
 }
 
+static inline bool
+of_pci_bridge_preserve_resources(struct device_node *node)
+{
+	return false;
+}
+
 static inline int pci_set_of_node(struct pci_dev *dev) { return 0; }
 static inline void pci_release_of_node(struct pci_dev *dev) { }
 static inline void pci_set_bus_of_node(struct pci_bus *bus) { }
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 1325fbae2f28..ceb9129823ee 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -15,6 +15,7 @@
 #include <linux/cpumask.h>
 #include <linux/aer.h>
 #include <linux/acpi.h>
+#include <linux/pci-acpi.h>
 #include <linux/hypervisor.h>
 #include <linux/irqdomain.h>
 #include <linux/pm_runtime.h>
@@ -889,6 +890,30 @@ static void pci_set_bus_msi_domain(struct pci_bus *bus)
 	dev_set_msi_domain(&bus->dev, d);
 }
 
+static bool pci_must_preserve_config(struct pci_host_bridge *host_bridge)
+{
+	if (ACPI_HANDLE(&host_bridge->dev)) {
+		union acpi_object *obj;
+
+		/*
+		 * Evaluate the "PCI Boot Configuration" _DSM Function.  If it
+		 * exists and returns 0, we must preserve any PCI resource
+		 * assignments made by firmware for this host bridge.
+		 */
+		obj = acpi_evaluate_dsm_typed(ACPI_HANDLE(&host_bridge->dev), &pci_acpi_dsm_guid,
+					      1, DSM_PCI_PRESERVE_BOOT_CONFIG, NULL,
+					      ACPI_TYPE_INTEGER);
+		if (obj && obj->integer.value == 0)
+			return true;
+		ACPI_FREE(obj);
+	}
+
+	if (host_bridge->dev.parent && host_bridge->dev.parent->of_node)
+		return of_pci_bridge_preserve_resources(host_bridge->dev.parent->of_node);
+
+	return false;
+}
+
 static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 {
 	struct device *parent = bridge->dev.parent;
@@ -983,6 +1008,9 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 	if (nr_node_ids > 1 && pcibus_to_node(bus) == NUMA_NO_NODE)
 		dev_warn(&bus->dev, "Unknown NUMA node; performance will be reduced\n");
 
+	/* Check if the boot configuration by FW needs to be preserved */
+	bridge->preserve_config = pci_must_preserve_config(bridge);
+
 	/* Coalesce contiguous windows */
 	resource_list_for_each_entry_safe(window, n, &resources) {
 		if (list_is_last(&window->node, &resources))
@@ -3074,20 +3102,18 @@ int pci_host_probe(struct pci_host_bridge *bridge)
 
 	bus = bridge->bus;
 
+	/* If we must preserve the resource configuration, claim now */
+	if (bridge->preserve_config)
+		pci_bus_claim_resources(bus);
+
 	/*
-	 * We insert PCI resources into the iomem_resource and
-	 * ioport_resource trees in either pci_bus_claim_resources()
-	 * or pci_bus_assign_resources().
+	 * Assign whatever was left unassigned. If we didn't claim above,
+	 * this will reassign everything.
 	 */
-	if (pci_has_flag(PCI_PROBE_ONLY)) {
-		pci_bus_claim_resources(bus);
-	} else {
-		pci_bus_size_bridges(bus);
-		pci_bus_assign_resources(bus);
+	pci_assign_unassigned_root_bus_resources(bus);
 
-		list_for_each_entry(child, &bus->children, node)
-			pcie_bus_configure_settings(child);
-	}
+	list_for_each_entry(child, &bus->children, node)
+		pcie_bus_configure_settings(child);
 
 	pci_bus_add_devices(bus);
 	return 0;
-- 
2.25.1

Re: [PATCH V6] PCI: Add support for preserving boot configuration

[Bjorn Helgaas]

On Thu, Apr 18, 2024 at 11:10:43PM +0530, Vidya Sagar wrote:
> Add support for preserving the boot configuration done by the
> platform firmware per host bridge basis, based on the presence of
> 'linux,pci-probe-only' property in the respective PCI host bridge
> device-tree node. It also unifies the ACPI and DT based boot flows
> in this regard.

This looks great; my only comments are:

  - It might make sense to move the _DSM evaluation to pci-acpi.c
    instead of probe.c.

  - There are a few different things going on (move _DSM, look at DT
    host bridge in addition to of_chosen, integrate ACPI and DT flows,
    tweak usage of PCI_PROBE_ONLY vs bridge->preserve_config, use
    pci_assign_unassigned_root_bus_resources() when we didn't before),
    and I think they could be split into multiple patches to make it
    easier to read.

I took a stab at splitting this, but didn't quite complete it.  I'll
post that as v7-incomplete, and if you compare with v6, you'll see
what's missing (the PCI_PROBE_ONLY and assign resources stuff --
there's some subtlety there that wasn't obvious to me).

Bjorn

[PATCH v7-incomplete 0/3] PCI: Add support for preserving boot configuration

[Bjorn Helgaas]

From: Bjorn Helgaas <bhelgaas@google.com>

This is Vidya's work; I started splitting it into separate patches.

This is based on v6
(https://lore.kernel.org/r/20240418174043.3750240-1-vidyas@nvidia.com) but
is missing a few pieces, so it's not complete yet.  I just wanted to show
the idea of what I had in mind.

The missing pieces are:

  - Set PCI_REASSIGN_ALL_BUS if !PCI_PROBE_ONLY

  - Use bridge->preserve_config instead of PCI_PROBE_ONLY

  - Change to use pci_assign_unassigned_root_bus_resources() instead of 
    pci_bus_size_bridge() and pci_bus_assign_resources()

Bjorn Helgaas (3):
  PCI: Move PRESERVE_BOOT_CONFIG _DSM evaluation to
    pci_register_host_bridge()
  PCI: of: Add of_pci_preserve_config() for per-host bridge support
  PCI: Unify ACPI and DT 'preserve config' support

 drivers/acpi/pci_root.c | 12 ---------
 drivers/pci/of.c        | 60 ++++++++++++++++++++++++++++++++---------
 drivers/pci/pci-acpi.c  | 22 +++++++++++++++
 drivers/pci/pci.h       | 12 +++++++++
 drivers/pci/probe.c     | 14 ++++++++++
 5 files changed, 95 insertions(+), 25 deletions(-)

-- 
2.34.1

[PATCH v7-incomplete 1/3] PCI: Move PRESERVE_BOOT_CONFIG _DSM evaluation to pci_register_host_bridge()

[Bjorn Helgaas]

From: Bjorn Helgaas <bhelgaas@google.com>

Move the PRESERVE_BOOT_CONFIG _DSM evaluation from acpi_pci_root_create()
to pci_register_host_bridge().

This will help unify the ACPI _DSM path and the DT-based
"linux,pci-probe-only" paths.

This should be safe because it happens earlier than it used to:

    acpi_pci_root_create
      pci_create_root_bus
        pci_register_host_bridge
  +       bridge->preserve_config = pci_preserve_config(bridge)
            pci_acpi_preserve_config
  +           acpi_evaluate_dsm_typed(DSM_PCI_PRESERVE_BOOT_CONFIG)
  -   acpi_evaluate_dsm_typed(DSM_PCI_PRESERVE_BOOT_CONFIG)

No functional change intended.
---
 drivers/acpi/pci_root.c | 12 ------------
 drivers/pci/pci-acpi.c  | 22 ++++++++++++++++++++++
 drivers/pci/pci.h       |  5 +++++
 drivers/pci/probe.c     | 11 +++++++++++
 4 files changed, 38 insertions(+), 12 deletions(-)

diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
index 58b89b8d950e..ddc2b3e89111 100644
--- a/drivers/acpi/pci_root.c
+++ b/drivers/acpi/pci_root.c
@@ -1008,7 +1008,6 @@ struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
 	int node = acpi_get_node(device->handle);
 	struct pci_bus *bus;
 	struct pci_host_bridge *host_bridge;
-	union acpi_object *obj;
 
 	info->root = root;
 	info->bridge = device;
@@ -1050,17 +1049,6 @@ struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
 	if (!(root->osc_ext_control_set & OSC_CXL_ERROR_REPORTING_CONTROL))
 		host_bridge->native_cxl_error = 0;
 
-	/*
-	 * Evaluate the "PCI Boot Configuration" _DSM Function.  If it
-	 * exists and returns 0, we must preserve any PCI resource
-	 * assignments made by firmware for this host bridge.
-	 */
-	obj = acpi_evaluate_dsm_typed(ACPI_HANDLE(bus->bridge), &pci_acpi_dsm_guid, 1,
-				      DSM_PCI_PRESERVE_BOOT_CONFIG, NULL, ACPI_TYPE_INTEGER);
-	if (obj && obj->integer.value == 0)
-		host_bridge->preserve_config = 1;
-	ACPI_FREE(obj);
-
 	acpi_dev_power_up_children_with_adr(device);
 
 	pci_scan_child_bus(bus);
diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
index 004575091596..9cc447da9475 100644
--- a/drivers/pci/pci-acpi.c
+++ b/drivers/pci/pci-acpi.c
@@ -119,6 +119,28 @@ phys_addr_t acpi_pci_root_get_mcfg_addr(acpi_handle handle)
 	return (phys_addr_t)mcfg_addr;
 }
 
+bool pci_acpi_preserve_config(struct pci_host_bridge *host_bridge)
+{
+	if (ACPI_HANDLE(&host_bridge->dev)) {
+		union acpi_object *obj;
+
+		/*
+		 * Evaluate the "PCI Boot Configuration" _DSM Function.  If it
+		 * exists and returns 0, we must preserve any PCI resource
+		 * assignments made by firmware for this host bridge.
+		 */
+		obj = acpi_evaluate_dsm_typed(ACPI_HANDLE(&host_bridge->dev),
+					      &pci_acpi_dsm_guid,
+					      1, DSM_PCI_PRESERVE_BOOT_CONFIG,
+					      NULL, ACPI_TYPE_INTEGER);
+		if (obj && obj->integer.value == 0)
+			return true;
+		ACPI_FREE(obj);
+	}
+
+	return false;
+}
+
 /* _HPX PCI Setting Record (Type 0); same as _HPP */
 struct hpx_type0 {
 	u32 revision;		/* Not present in _HPP */
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 17fed1846847..180d3907b543 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -734,6 +734,7 @@ static inline void pci_restore_aer_state(struct pci_dev *dev) { }
 #endif
 
 #ifdef CONFIG_ACPI
+bool pci_acpi_preserve_config(struct pci_host_bridge *bridge);
 int pci_acpi_program_hp_params(struct pci_dev *dev);
 extern const struct attribute_group pci_dev_acpi_attr_group;
 void pci_set_acpi_fwnode(struct pci_dev *dev);
@@ -747,6 +748,10 @@ int acpi_pci_wakeup(struct pci_dev *dev, bool enable);
 bool acpi_pci_need_resume(struct pci_dev *dev);
 pci_power_t acpi_pci_choose_state(struct pci_dev *pdev);
 #else
+static inline bool pci_acpi_preserve_config(struct pci_host_bridge *bridge)
+{
+	return false;
+}
 static inline int pci_dev_acpi_reset(struct pci_dev *dev, bool probe)
 {
 	return -ENOTTY;
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 1325fbae2f28..ee086d029450 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -889,6 +889,14 @@ static void pci_set_bus_msi_domain(struct pci_bus *bus)
 	dev_set_msi_domain(&bus->dev, d);
 }
 
+static bool pci_preserve_config(struct pci_host_bridge *host_bridge)
+{
+	if (pci_acpi_preserve_config(host_bridge))
+		return true;
+
+	return false;
+}
+
 static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 {
 	struct device *parent = bridge->dev.parent;
@@ -983,6 +991,9 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 	if (nr_node_ids > 1 && pcibus_to_node(bus) == NUMA_NO_NODE)
 		dev_warn(&bus->dev, "Unknown NUMA node; performance will be reduced\n");
 
+	/* Check if the boot configuration by FW needs to be preserved */
+	bridge->preserve_config = pci_preserve_config(bridge);
+
 	/* Coalesce contiguous windows */
 	resource_list_for_each_entry_safe(window, n, &resources) {
 		if (list_is_last(&window->node, &resources))
-- 
2.34.1

Re: [PATCH v7-incomplete 1/3] PCI: Move PRESERVE_BOOT_CONFIG _DSM evaluation to pci_register_host_bridge()

[Andy Shevchenko]

Sun, Apr 21, 2024 at 02:09:12PM -0500, Bjorn Helgaas kirjoitti:
> From: Bjorn Helgaas <bhelgaas@google.com>
> 
> Move the PRESERVE_BOOT_CONFIG _DSM evaluation from acpi_pci_root_create()
> to pci_register_host_bridge().
> 
> This will help unify the ACPI _DSM path and the DT-based
> "linux,pci-probe-only" paths.

...

> +bool pci_acpi_preserve_config(struct pci_host_bridge *host_bridge)
> +{
> +	if (ACPI_HANDLE(&host_bridge->dev)) {

Wouldn't the below looks nicer if you invert the conditional?

	handle = ACPI_HANDLE(...);

	if (!handle)
		return false;

	...

> +		union acpi_object *obj;
> +
> +		/*
> +		 * Evaluate the "PCI Boot Configuration" _DSM Function.  If it
> +		 * exists and returns 0, we must preserve any PCI resource
> +		 * assignments made by firmware for this host bridge.
> +		 */
> +		obj = acpi_evaluate_dsm_typed(ACPI_HANDLE(&host_bridge->dev),
> +					      &pci_acpi_dsm_guid,
> +					      1, DSM_PCI_PRESERVE_BOOT_CONFIG,
> +					      NULL, ACPI_TYPE_INTEGER);
> +		if (obj && obj->integer.value == 0)
> +			return true;
> +		ACPI_FREE(obj);
> +	}
> +
> +	return false;
> +}


-- 
With Best Regards,
Andy Shevchenko

[PATCH v7-incomplete 2/3] PCI: of: Add of_pci_preserve_config() for per-host bridge support

[Bjorn Helgaas]

From: Bjorn Helgaas <bhelgaas@google.com>

Add of_pci_preserve_config() to look for the "linux,pci-probe-only"
property under a specified node.  If it's not found there, look under
"of_chosen" in addition.

If the caller didn't specify a node, look under "of_chosen".

With a future patch, this will support "linux,pci-probe-only" on a per host
bridge basis based on the presence of the property in the respective PCI
host bridge DT node.

Implement of_pci_check_probe_only() using of_pci_preserve_config().
---
 drivers/pci/of.c  | 60 +++++++++++++++++++++++++++++++++++++----------
 drivers/pci/pci.h |  7 ++++++
 2 files changed, 54 insertions(+), 13 deletions(-)

diff --git a/drivers/pci/of.c b/drivers/pci/of.c
index 51e3dd0ea5ab..d21c0bed36f3 100644
--- a/drivers/pci/of.c
+++ b/drivers/pci/of.c
@@ -233,28 +233,62 @@ int of_get_pci_domain_nr(struct device_node *node)
 }
 EXPORT_SYMBOL_GPL(of_get_pci_domain_nr);
 
+/**
+ * of_pci_preserve_config - Return true if the boot configuration needs to
+ *                          be preserved
+ * @node: Device tree node.
+ *
+ * This function looks for "linux,pci-probe-only" property for a given
+ * PCI controller's node and returns true if found. It will also look in the
+ * chosen node if the property is not found in the given controller's node.
+ * Having this property ensures that the kernel doesn't reconfigure the
+ * BARs and bridge windows that are already done by the platform firmware.
+ *
+ * Return: true if the property exists false otherwise.
+ */
+bool of_pci_preserve_config(struct device_node *node)
+{
+	u32 val = 0;
+	int ret;
+
+	if (!node) {
+		pr_warn("device node is NULL, trying with of_chosen\n");
+		node = of_chosen;
+	}
+
+retry:
+	ret = of_property_read_u32(node, "linux,pci-probe-only", &val);
+	if (ret) {
+		if (ret == -ENODATA || ret == -EOVERFLOW) {
+			pr_warn("Incorrect value for linux,pci-probe-only in %pOF, ignoring\n",
+				node);
+			return false;
+		}
+		if (ret == -EINVAL) {
+			if (node == of_chosen)
+				return false;
+
+			node = of_chosen;
+			goto retry;
+		}
+	}
+
+	if (val)
+		return true;
+	else
+		return false;
+}
+
 /**
  * of_pci_check_probe_only - Setup probe only mode if linux,pci-probe-only
  *                           is present and valid
  */
 void of_pci_check_probe_only(void)
 {
-	u32 val;
-	int ret;
-
-	ret = of_property_read_u32(of_chosen, "linux,pci-probe-only", &val);
-	if (ret) {
-		if (ret == -ENODATA || ret == -EOVERFLOW)
-			pr_warn("linux,pci-probe-only without valid value, ignoring\n");
-		return;
-	}
-
-	if (val)
+	if (of_pci_preserve_config(of_chosen))
 		pci_add_flags(PCI_PROBE_ONLY);
 	else
 		pci_clear_flags(PCI_PROBE_ONLY);
-
-	pr_info("PROBE_ONLY %s\n", val ? "enabled" : "disabled");
 }
 EXPORT_SYMBOL_GPL(of_pci_check_probe_only);
 
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 180d3907b543..feedbedd65df 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -650,6 +650,7 @@ int of_pci_get_max_link_speed(struct device_node *node);
 u32 of_pci_get_slot_power_limit(struct device_node *node,
 				u8 *slot_power_limit_value,
 				u8 *slot_power_limit_scale);
+bool of_pci_preserve_config(struct device_node *node);
 int pci_set_of_node(struct pci_dev *dev);
 void pci_release_of_node(struct pci_dev *dev);
 void pci_set_bus_of_node(struct pci_bus *bus);
@@ -688,6 +689,12 @@ of_pci_get_slot_power_limit(struct device_node *node,
 	return 0;
 }
 
+static inline bool
+of_pci_preserve_config(struct device_node *node)
+{
+	return false;
+}
+
 static inline int pci_set_of_node(struct pci_dev *dev) { return 0; }
 static inline void pci_release_of_node(struct pci_dev *dev) { }
 static inline void pci_set_bus_of_node(struct pci_bus *bus) { }
-- 
2.34.1

[PATCH v7-incomplete 3/3] PCI: Unify ACPI and DT 'preserve config' support

[Bjorn Helgaas]

From: Bjorn Helgaas <bhelgaas@google.com>

---
 drivers/pci/probe.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index ee086d029450..2c232c22d6af 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -894,6 +894,9 @@ static bool pci_preserve_config(struct pci_host_bridge *host_bridge)
 	if (pci_acpi_preserve_config(host_bridge))
 		return true;
 
+	if (host_bridge->dev.parent && host_bridge->dev.parent->of_node)
+		return of_pci_preserve_config(host_bridge->dev.parent->of_node);
+
 	return false;
 }
 
-- 
2.34.1

Re: [PATCH v7-incomplete 3/3] PCI: Unify ACPI and DT 'preserve config' support

[Andy Shevchenko]

Sun, Apr 21, 2024 at 02:09:14PM -0500, Bjorn Helgaas kirjoitti:

...

> +	if (host_bridge->dev.parent && host_bridge->dev.parent->of_node)
> +		return of_pci_preserve_config(host_bridge->dev.parent->of_node);

If you need fwnode or of_node from struct device, please avoid direct
dereference, we have

dev_fwnode()
of_fwnode_handle()
dev_of_node()

-- 
With Best Regards,
Andy Shevchenko