Re: [PATCH v4 2/2] PCI: Don't assume root ports from > 2015 are power manageable

[Mika Westerberg <mika.westerberg@linux.intel.com>]

On Wed, May 24, 2023 at 02:07:26PM -0500, Mario Limonciello wrote:
> Using a USB keyboard or mouse to wakeup the system from s2idle fails when
> that XHCI device is connected to a USB-C port for an AMD USB4 router.

nit: I think the correct is "xHCI" but no need to spin a new version
just for that.

> Due to commit 9d26d3a8f1b0 ("PCI: Put PCIe ports into D3 during suspend")
> all PCIe ports go into D3 during s2idle.
> 
> When specific root ports are put into D3 over s2idle on some AMD platforms
> it is not possible for the platform to properly identify wakeup sources.
> This happens whether the root port goes into D3hot or D3cold.
> 
> Comparing registers between Linux and Windows 11 this behavior to put
> these specific root ports into D3 at suspend is unique to Linux. On an
> affected system Windows does not put those specific root ports into D3
> over Modern Standby.
> 
> Windows doesn't put the root ports into D3 because root ports are not
> power manageable.

Probably better is to say:

 Windows avoids putting Root Ports that are not power manageable (e.g do
 not have platform firmware support) into low power states.

but again no need to respin just for that.

> Linux shouldn't assume root ports support D3 just because they're on a
> machine newer than 2015, the ports should also be deemed power manageable.
> Add an extra check explicitly for root ports to ensure D3 isn't selected
> for these ports.
> 
> Fixes: 9d26d3a8f1b0 ("PCI: Put PCIe ports into D3 during suspend")
> Reported-by: Iain Lane <iain@orangesquash.org.uk>
> Closes: https://forums.lenovo.com/t5/Ubuntu/Z13-can-t-resume-from-suspend-with-external-USB-keyboard/m-p/5217121
> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>

Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>