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

Vidya Sagar
2024-02-22T12:41:43Z

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