[PATCH v5 1/2] Add rev 2 check for PRESERVE_BOOT_CONFIG function

From: Zhou Shengqing
Date: Thu Mar 13 2025 - 06:07:47 EST


Per PCI Firmware Specification Revision 3.3 Table 4-7 _DSM Definitions
for PCI. Preserve PCI Boot Configuration Initial Revision ID changed to 2.

And add acpi_check_dsm() for DSM_PCI_PRESERVE_BOOT_CONFIG.

Signed-off-by: Zhou Shengqing <zhoushengqing@xxxxxxxxxxx>
---
v5:follow Bjorn advice, add acpi_check_dsm for PCI _DSM.
v4:Initialize *obj to NULL.
v3:try revision id 1 first, then try revision id 2.
v2:add Fixes tag.

Fixes: 9d7d5db8e78e ("PCI: Move PRESERVE_BOOT_CONFIG _DSM evaluation to pci_re")
---
drivers/pci/pci-acpi.c | 43 ++++++++++++++++++++++++++++++------------
1 file changed, 31 insertions(+), 12 deletions(-)

diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
index af370628e583..4f9e0548c96d 100644
--- a/drivers/pci/pci-acpi.c
+++ b/drivers/pci/pci-acpi.c
@@ -122,24 +122,43 @@ phys_addr_t acpi_pci_root_get_mcfg_addr(acpi_handle handle)

bool pci_acpi_preserve_config(struct pci_host_bridge *host_bridge)
{
- if (ACPI_HANDLE(&host_bridge->dev)) {
- union acpi_object *obj;
+ bool rc = 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.
- */
+ if (!ACPI_HANDLE(&host_bridge->dev))
+ return false;
+
+ /*
+ * 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.
+ *
+ * Per PCI Firmware r3.2, released Jan 26, 2015,
+ * DSM_PCI_PRESERVE_BOOT_CONFIG Revision ID is 1. But PCI Firmware r3.3,
+ * released Jan 20, 2021, changed sec 4.6.5 to say
+ * "lowest valid Revision ID value: 2". So check rev 1 first, then rev 2.
+ */
+ if (acpi_check_dsm(ACPI_HANDLE(&host_bridge->dev),
+ &pci_acpi_dsm_guid, 1, BIT(DSM_PCI_PRESERVE_BOOT_CONFIG))) {
obj = acpi_evaluate_dsm_typed(ACPI_HANDLE(&host_bridge->dev),
- &pci_acpi_dsm_guid,
- 1, DSM_PCI_PRESERVE_BOOT_CONFIG,
- NULL, ACPI_TYPE_INTEGER);
+ &pci_acpi_dsm_guid,
+ 1, DSM_PCI_PRESERVE_BOOT_CONFIG,
+ NULL, ACPI_TYPE_INTEGER);
if (obj && obj->integer.value == 0)
- return true;
+ rc = true;
+ ACPI_FREE(obj);
+ } else if (acpi_check_dsm(ACPI_HANDLE(&host_bridge->dev),
+ &pci_acpi_dsm_guid, 2, BIT(DSM_PCI_PRESERVE_BOOT_CONFIG))) {
+ obj = acpi_evaluate_dsm_typed(ACPI_HANDLE(&host_bridge->dev),
+ &pci_acpi_dsm_guid,
+ 2, DSM_PCI_PRESERVE_BOOT_CONFIG,
+ NULL, ACPI_TYPE_INTEGER);
+ if (obj && obj->integer.value == 0)
+ rc = true;
ACPI_FREE(obj);
}

- return false;
+ return rc;
}

/* _HPX PCI Setting Record (Type 0); same as _HPP */
--
2.39.2