[PATCH V1 0/2] Add support to preserve boot config in the DT flow

[PATCH V1 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.

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                              | 15 +++++++++++++++
 drivers/pci/probe.c                           |  2 +-
 include/linux/of_pci.h                        |  6 ++++++
 5 files changed, 30 insertions(+), 2 deletions(-)

-- 
2.25.1

[PATCH V1 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>
---
 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

[PATCH V1 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.

Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
---
 drivers/pci/controller/pci-host-common.c |  5 ++++-
 drivers/pci/of.c                         | 15 +++++++++++++++
 drivers/pci/probe.c                      |  2 +-
 include/linux/of_pci.h                   |  6 ++++++
 4 files changed, 26 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..3216d4557212 100644
--- a/drivers/pci/of.c
+++ b/drivers/pci/of.c
@@ -258,6 +258,21 @@ 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
+ *
+ * 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.
+ */
+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..a408e54128c6 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 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 V1 2/2] PCI: Add support for "preserve-boot-config" property

[kernel test robot]

Hi Vidya,

kernel test robot noticed the following build warnings:

[auto build test WARNING on pci/next]
[also build test WARNING on pci/for-linus linus/master v6.7 next-20240109]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Vidya-Sagar/dt-bindings-Add-PCIe-preserve-boot-config-property/20240109-130938
base:   https://git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git next
patch link:    https://lore.kernel.org/r/20240109050648.1347255-3-vidyas%40nvidia.com
patch subject: [PATCH V1 2/2] PCI: Add support for "preserve-boot-config" property
config: alpha-allnoconfig (https://download.01.org/0day-ci/archive/20240110/202401100554.kaCFjM87-lkp@intel.com/config)
compiler: alpha-linux-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240110/202401100554.kaCFjM87-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202401100554.kaCFjM87-lkp@intel.com/

All warnings (new ones prefixed by >>):

   In file included from drivers/pci/probe.c:11:
>> include/linux/of_pci.h:31:13: warning: 'of_pci_check_preserve_boot_config' defined but not used [-Wunused-function]
      31 | static bool of_pci_check_preserve_boot_config(struct device_node *node)
         |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


vim +/of_pci_check_preserve_boot_config +31 include/linux/of_pci.h

    30	
  > 31	static bool of_pci_check_preserve_boot_config(struct device_node *node)
    32	{
    33		return false;
    34	}
    35	#endif
    36	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH V1 2/2] PCI: Add support for "preserve-boot-config" property

[kernel test robot]

Hi Vidya,

kernel test robot noticed the following build warnings:

[auto build test WARNING on pci/next]
[also build test WARNING on pci/for-linus linus/master v6.7 next-20240109]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Vidya-Sagar/dt-bindings-Add-PCIe-preserve-boot-config-property/20240109-130938
base:   https://git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git next
patch link:    https://lore.kernel.org/r/20240109050648.1347255-3-vidyas%40nvidia.com
patch subject: [PATCH V1 2/2] PCI: Add support for "preserve-boot-config" property
config: arc-allnoconfig (https://download.01.org/0day-ci/archive/20240110/202401101015.Dch3YIjG-lkp@intel.com/config)
compiler: arc-elf-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240110/202401101015.Dch3YIjG-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202401101015.Dch3YIjG-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> drivers/pci/of.c:271: warning: Function parameter or struct member 'node' not described in 'of_pci_check_preserve_boot_config'


vim +271 drivers/pci/of.c

   260	
   261	/**
   262	 * of_pci_check_preserve_boot_config - Return true if the boot configuration
   263	 *                                     needs to be preserved
   264	 *
   265	 * This function looks for a property called "preserve-boot-config" for a given
   266	 * PCIe controller's node and returns true if found. Having this property
   267	 * for a PCIe controller ensures that the kernel doesn't re-enumerate and
   268	 * reconfigure the BAR resources that are already done by the platform firmware.
   269	 */
   270	bool of_pci_check_preserve_boot_config(struct device_node *node)
 > 271	{
   272		return of_property_read_bool(node, "preserve-boot-config");
   273	}
   274	EXPORT_SYMBOL_GPL(of_pci_check_preserve_boot_config);
   275	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki