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

Vidya Sagar
2024-01-10T03:08:07Z

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