Bjorn: so, given this and other comments, what's the decision on this patch? Any
particular changes I should do for it to be accepted?
On Fri, 2021-05-07 at 17:08 +0300, Konstantin Kharlamov wrote:
> On Fri, 2021-05-07 at 08:30 -0500, Bjorn Helgaas wrote:
> > 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.
>
> I did some research, and found that s2idle was first introduced in 2013 in
> commit 7e73c5ae6e799 (except it wasn't called "s2idle", by that name it goes
> since around 2016 as Lukas mentioned. In 7e73c5ae6e799 it is called "freeze").
> This is before 1df5172c5c25 which was added in 2014, so I guess we can add a:
>
> Fixes: 1df5172c5c25 ("PCI: Suspend/resume quirks for Apple
> thunderbolt")
>
> > 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.
>
> Sorry, I can't comment anything regarding AML and power management in general
> since I am really new to all of this. However, regarding the usage of the
> `pm_suspend_via_firmware()`: yeah, I also think it is unclear what this does,
> and I was thinking about adding a wrapper function something like
> `is_s2idle()` to the suspend.h, which would simply call
> `pm_suspend_via_firmware` internally. I didn't do that because I thought that
> usage of pm_suspend_via_firmware() for that task is just something people
> working with power management are supposed to know, but if someone else
> questions it too, I can make such wrapper, it's just a 3 lines-of-code change.
>
> FWIW, originally I found out that pm_suspend_via_firmware() can be used for
> detecting s2idle by simply asking about it on linux-pm:
> https://marc.info/?l=linux-pm&m=162029296108775&w=2
>
