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

[Zhou Shengqing <zhoushengqing@xxxxxxxxxxx>]

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