Re: [PATCH] PCI: don't power-off apple thunderbolt controller on s2idle

[Lukas Wunner <lukas@wunner.de>]

On Thu, May 06, 2021 at 04:48:42PM -0500, Bjorn Helgaas wrote:
> On Thu, May 06, 2021 at 08:38:20PM +0300, Konstantin Kharlamov wrote:
> > On Macbook 2013 resuming from s2idle results in external monitor no
> > longer being detected, and dmesg having errors like:
> > 
> >     pcieport 0000:06:00.0: can't change power state from D3hot to D0 (config space inaccessible)
> > 
> > and a stacktrace. The reason turned out that the hw that the quirk
> > powers off does not get powered on back on resume.
> 
> quirk_apple_poweroff_thunderbolt() was added in 2014 by 1df5172c5c25
> ("PCI: Suspend/resume quirks for Apple thunderbolt").  It claims
> "power is automatically restored before resume," so there must be
> something special about s2idle that prevents the power-on.

With s2idle, the machine isn't suspended via ACPI, so the AML code
which powers the controller off isn't executed.  The dance to prepare
the controller for power-off consequently isn't necessary but rather
harmful.

To get the same power savings as with ACPI suspend, the controller
needs to be powered off via runtime suspend.  I posted patches for
that back in 2016.  I'm using them on my laptop, they need some
polishing and rebasing before I can repost them due to massive
changes that have happened in the thunderbolt driver in the meantime.
Without these patches, the controller sucks 1.5W of power in s2idle.

> Obviously the *hardware* hasn't changed since 1df5172c5c25.  Is s2idle
> something that wasn't tested back then, or is this problem connected
> to an s2idle change since then?  Can we identify a commit that
> introduced this problem?  That would help with backporting or stable
> tags.

Yes I believe the quirk predates the introduction of s2idle by a couple
of years.

> > Signed-off-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>

Reviewed-by: Lukas Wunner <lukas@wunner.de>

The patch looks fine to me.

Thanks,

Lukas