On Fri, May 07, 2021 at 12:07:38AM +0200, Lukas Wunner wrote:
> 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.
In an ideal world, we would know which commit introduced s2idle and
hence the possibility of hitting this bug, and we would add a Fixes:
tag for that commit so we could connect this fix with it.
Apart from that, what I don't like about this (and about the original
1df5172c5c25) is that there's no connection to a spec or to documented
behavior of the device or of suspend/resume.
For example, "With s2idle, the machine isn't suspended via ACPI, so
the AML code which powers the controller off isn't executed." AFAICT
that isn't actually a required, documented property of s2idle, but
rather it reaches into the internal implementation.
The code comment "If suspend mode is s2idle, power won't get restored
on resume" is similar. !pm_suspend_via_firmware() tells us that
platform firmware won't be invoked. But the connection between *that*
and "power won't get restored" is unexplained.
> > > Signed-off-by: Konstantin Kharlamov <Hi-Angel@xxxxxxxxx>
>
> Reviewed-by: Lukas Wunner <lukas@xxxxxxxxx>
Thanks for looking at this!
Bjorn
