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    SubjectRe: [PATCH v4] PCI: Call _REG when transitioning D-states
    On Wed, Jun 21, 2023 at 05:52:52PM -0500, Limonciello, Mario wrote:
    > On 6/21/2023 5:28 PM, Bjorn Helgaas wrote:
    > > On Tue, Jun 20, 2023 at 09:04:51AM -0500, Mario Limonciello wrote:
    > > > Section 6.5.4 of the ACPI 6.4 spec describes how AML is unable to access
    > > > an OperationRegion unless `_REG` has been called.
    > > > ...

    > > > It is reported that ASMedia PCIe GPIO controllers fail
    > > > functional tests after the system has returning from suspend (S3
    > > > or s2idle). This is because the BIOS checks whether the OSPM has
    > > > called the `_REG` method to determine whether it can interact
    > > > with the OperationRegion assigned to the device as part of the
    > > > other AML called for the device.

    > I double checked a BIOS debug log which shows ACPI calls
    > to confirm and didn't see a single _REG call for any device
    > before this patch across a boot/suspend/resume cycle.

    Sorry to follow up on this again.

    The commit log says these GPIO controllers fail functional tests after
    returning from suspend. Do those functional tests pass *before*
    suspend? If so, why?

    Without this patch, we *never* call _REG, so the fact that calling
    _REG when we return the device to D0 while resuming fixes something
    suggests that it might have been broken even before the suspend.

    Bjorn

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