On Wed, Jan 11, 2023 at 11:56:05AM +0100, Rafael J. Wysocki wrote:
> On Tue, Jan 10, 2023 at 9:55 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
> > On Mon, Jan 02, 2023 at 05:59:36PM +0100, Rafael J. Wysocki wrote:
> > > On Monday, January 2, 2023 5:34:19 PM CET Rafael J. Wysocki wrote:
> > > ...
> >
> > > > I don't really think that Root Port support is required for a bridge below
> > > > a Root Port if that bridge itself is power-manageable via ACPI. Moreover,
> > > > I don't think that the _S0W of a Root Port has any bearing on devices below
> > > > it that have their own _S0W.
> > > >
> > > > So what we really want appears to be to evaluate _S0W for the target bridge,
> > > > regardless of whether or not it is a Root Port, and return 'false' if that
> > > > produces D2 or a shallower power state. Otherwise, we can do what we've
> > > > done so far.
> >
> > > +bool acpi_dev_no_wakeup_from_d3(struct acpi_device *adev)
> > > +{
> > > + unsigned long long state;
> > > + acpi_status status;
> > > +
> > > + status = acpi_evaluate_integer(adev->handle, "_S0W", NULL, &state);
> > > + return ACPI_SUCCESS(status) && state < ACPI_STATE_D3_HOT;
> >
> > This returns "false" (i.e., "yes, device can signal wakeup from D3")
> > if _S0W doesn't exist. Is that right?
>
> Yes, it is.
>
> The reason why I did it that way was because the bridge cannot signal
> wakeup from D3 if both the following conditions take place:
>
> 1. There is _S0W and it can be evaluated successfully.
> 2. _S0W produces D2 or a shallower power state.
>
> In particular, if 1 is not the case, it is still not clear whether or
> not the bridge can signal wakeup from D3 and additional checks are
> needed.
>
> > I think this might be less confusing as:
> >
> > bool acpi_dev_can_wake_from_d3(struct acpi_device *adev)
> > {
> > status = acpi_evaluate_integer(adev->handle, "_S0W", NULL, &state);
> > return ACPI_SUCCESS(status) && state >= ACPI_STATE_D3_HOT;
> > }
>
> So I don't think the above will work, because
> !acpi_dev_can_wake_from_d3(adev) is also true if _S0W is not present,
> for example, in which case acpi_pci_bridge_d3() should not return
> 'false' right away.
OK, that makes sense, thanks!
> However, the additional function can simply return the value produced
> by _S0W or ACPI_STATE_UNKNOWN on all errors and its caller can do the
> checks as needed which is done here:
>
> https://patchwork.kernel.org/project/linux-acpi/patch/5659681.DvuYhMxLoT@kreacher/
>
> (posted as a proper patch, because I wanted patchwork to pick it up).
>
> I've also picked up the idea of using rpadev for representing the ACPI
> companion of the Root Port in acpi_pci_bridge_d3().
>
> Cheers!
