On Thu, Mar 13, 2025 at 11:07 AM Zhou Shengqing
<zhoushengqing@xxxxxxxxxxx> wrote:
>
> 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;
+ u64 rev;
>
> - /*
> - * 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.
> + */
+ for (rev = 1; rev <= 2; rev++) {
+ if (!acpi_check_dsm(ACPI_HANDLE(&host_bridge->dev),
&pci_acpi_dsm_guid,
+ rev, BIT(DSM_PCI_PRESERVE_BOOT_CONFIG)))
+ continue;
+
+ obj =
acpi_evaluate_dsm_typed(ACPI_HANDLE(&host_bridge->dev), ,
&pci_acpi_dsm_guid,
+ rev, BIT(DSM_PCI_PRESERVE_BOOT_CONFIG));
+ if (obj && obj->integer.value == 0)
+ rc = true;
+
+ ACPI_FREE(obj);
+
+ if (rc)
+ return true;
+ }
+
+ return false;
would achieve the same with fewer lines of code and less code
duplication if I'm not mistaken.
> + 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 */
> --
