On Thu, Feb 27, 2025 at 6:40 PM Bjorn Helgaas wrote:
> On Mon, Dec 16, 2024 at 05:27:51AM +0000, Zhou Shengqing 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.
> > But the code remains unchanged, still 1.
> >
> > v4:Initialize *obj to NULL.
> > v3:try revision id 1 first, then try revision id 2.
> > v2:add Fixes tag.
>
> Thanks for working on this issue.
>
> - Thanks for the revision history. For future posts, put it below
> the "---" line so it's in the email but not part of the commit log.
>
> - I think there's a leak in pci_acpi_preserve_config() because it
> doesn't free "obj" before it returns true. If you agree, add a
> preparatory patch to fix this.
>
> - Add a preparatory patch to return false early in
> pci_acpi_preserve_config() if !ACPI_HANDLE(&host_bridge->dev) so
> the body of the function is unindented, similar to what
> acpi_pci_add_bus() does.
>
> - Add another preparatory patch that adds acpi_check_dsm() of the
> desired function/rev ID for DSM_PCI_PRESERVE_BOOT_CONFIG,
> DSM_PCI_POWER_ON_RESET_DELAY, DSM_PCI_DEVICE_READINESS_DURATIONS.
> Move the "Evaluate PCI Boot Configuration" comment above the
> acpi_check_dsm() since it applies to the whole function, not just
> the rev 1 code in this patch.
>
> - Rework this patch so it only adds acpi_check_dsm() and
> acpi_evaluate_dsm_typed() for rev 2.
Could you please explain this in more detail? Do you mean we don't need to
consider rev 1 anymore?
>
> - Throughout, wrap code and comments to fit in 80 columns because
> that's the convention for the rest of the file.
>
> - You can use "BIT(DSM_PCI_PRESERVE_BOOT_CONFIG)" and similar
> instead of "1ULL << DSM_PCI_PRESERVE_BOOT_CONFIG" when calling
> acpi_check_dsm().
>
> - Add a [0/n] cover letter when posting the series. Each patch
> should be a response to the cover letter. "git format-patch" and
> "git send-email" will do that for you automatically.
>
> > Fixes: 9d7d5db8e78e ("PCI: Move PRESERVE_BOOT_CONFIG _DSM evaluation to pci_register_host_bridge()")
> >
> > Signed-off-by: Zhou Shengqing <zhoushengqing@xxxxxxxxxxx>
> > ---
> > drivers/pci/pci-acpi.c | 42 ++++++++++++++++++++++++++++++++----------
> > 1 file changed, 32 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
> > index af370628e583..f805cd134019 100644
> > --- a/drivers/pci/pci-acpi.c
> > +++ b/drivers/pci/pci-acpi.c
> > @@ -123,19 +123,41 @@ 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;
> > + union acpi_object *obj = NULL;
> >
> > /*
> > - * 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 try revision 1
> > + * first for old platform, then try revision 2.
> > */
> > - 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;
> > + if (acpi_check_dsm(ACPI_HANDLE(&host_bridge->dev), &pci_acpi_dsm_guid, 1,
> > + 1ULL << DSM_PCI_PRESERVE_BOOT_CONFIG)) {
> > + /*
> > + * 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;
> > + }
> > +
> > + if (acpi_check_dsm(ACPI_HANDLE(&host_bridge->dev), &pci_acpi_dsm_guid, 2,
> > + 1ULL << 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)
> > + return true;
> > + }
> > +
> > ACPI_FREE(obj);
> > }
> >
> > --
> > 2.39.2
> >
