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

Vidya Sagar
2024-04-18T17:41:27Z

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