From: Konstantin Kharlamov <email@example.com>
To: Bjorn Helgaas <firstname.lastname@example.org>,
"Rafael J. Wysocki" <email@example.com>
Cc: Lukas Wunner <firstname.lastname@example.org>,
Linux PCI <email@example.com>,
"Rafael J. Wysocki" <firstname.lastname@example.org>,
Andreas Noever <email@example.com>,
Linux PM <firstname.lastname@example.org>
Subject: Re: [PATCH] PCI: don't power-off apple thunderbolt controller on s2idle
Date: Fri, 21 May 2021 02:28:28 +0300 [thread overview]
Message-ID: <email@example.com> (raw)
Thank you very much. Well send then a v2 with the comment in a minute.
On Thu, 2021-05-20 at 14:49 -0500, Bjorn Helgaas wrote:
> On Thu, May 20, 2021 at 01:54:05PM +0200, Rafael J. Wysocki wrote:
> > On Thu, May 20, 2021 at 1:27 PM Rafael J. Wysocki <firstname.lastname@example.org> wrote:
> > > On Wed, May 19, 2021 at 9:48 PM Bjorn Helgaas <email@example.com> wrote:
> > > > On Wed, May 19, 2021 at 09:12:26PM +0200, Rafael J. Wysocki wrote:
> > > > > The problem is related to the fact that in s2idle the platform
> > > > > firmware does not finalize the suspend transition and, consequently,
> > > > > it doesn't initiate the resume transition. Therefore whatever power
> > > > > state the device was left in during suspend must be dealt with during
> > > > > the subsequent resume. Hence, if whatever is done by SXIO/SXFP/SXLF
> > > > > in the suspend path cannot be reversed in the resume path by the
> > > > > kernel (because there is no known method to do that), they should not
> > > > > be invoked. And that's exactly because the platform firmware will not
> > > > > finalize the suspend transition which is indicated by
> > > > > PM_SUSPEND_FLAG_FW_SUSPEND being unset.
> > > >
> > > > How can we connect "if (!pm_suspend_via_firmware())" in this patch
> > > > with the fact that firmware doesn't finalize suspend (and consequently
> > > > does not reverse things in resume)?
> > > >
> > > > I don't see any use of pm_suspend_via_firmware() or
> > > > PM_SUSPEND_FLAG_FW_SUSPEND that looks relevant.
> > >
> > > First of all, there is a kerneldoc comment next to
> > > pm_suspend_via_firmware() which is relevant. Especially the last
> > > paragraph of that comment applies directly to the case at hand IMV.
> I do read kerneldoc, but I *rely* on the code, and it's nice when I
> can match up the kerneldoc with what the code is doing :)
> Part of my confusion is that "passing control to platform firmware"
> isn't particularly useful in itself because it doesn't give a clue
> about what firmware is *doing*. Without knowing what it does, we
> can't reason about how kernel's actions interact with firmware's
> > BTW, the problem at hand is not that s2idle in particular needs to be
> > treated in a special way (this appears to be the source of all
> > confusion here). The problem is that the kernel cannot undo the
> > SXIO/SXFP/SXLF magic without passing control to the platform firmware.
> I assume this is really a case of "the kernel doesn't know *what* to
> do, but platform firmware does," so in principle the kernel *could*
> undo the SXIO/SXFP/SXLF magic if it knew what to do.
> > And "passing control to the platform firmware" doesn't mean "executing
> > some AML" here, because control remains in the kernel when AML is
> > executed. "Passing control to the platform firmware" means letting
> > some native firmware code (like SMM code) run which happens at the end
> > of S2/S3/S4 suspend transitions and it does not happen during S1
> > (standby) and s2idle suspend transitions.
> > That's why using SXIO/SXFP/SXLF is only valid during S2/S3/S4 suspend
> > transitions and it is not valid during s2idle and S1 suspend
> > transitions (and yes, S1 is also affected, so s2idle is not special in
> > that respect at all).
> > IMO the changelog of the patch needs to be rewritten, but the code
> > change made by it is reasonable.
> So IIUC the comment should say something like:
> SXIO/SXFP/SXLF turns off power to the Thunderbolt controller. We
> don't know how to turn it back on again, but firmware does, so we
> can only use SXIO/SXFP/SXLF if we're suspending via firmware.
> Actually, it sounds like the important thing is that we rely on the
> firmware *resume* path to turn on the power again.
> pm_resume_via_firmware() *sounds* like it would be appropriate, but
> the kerneldoc says that's for use after resume, and it tells us
> whether firmware has *already* handled the wakeup event. And
> PM_SUSPEND_FLAG_FW_RESUME isn't set until after we've run these
> suspend_late fixups, so it wouldn't work here.
next prev parent reply other threads:[~2021-05-20 23:28 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-06 17:38 [PATCH] PCI: don't power-off apple thunderbolt controller on s2idle Konstantin Kharlamov
2021-05-06 21:48 ` Bjorn Helgaas
2021-05-06 22:07 ` Lukas Wunner
2021-05-07 9:51 ` Rafael J. Wysocki
2021-05-08 8:48 ` Lukas Wunner
2021-05-07 13:30 ` Bjorn Helgaas
2021-05-07 14:08 ` Konstantin Kharlamov
2021-05-12 20:36 ` Konstantin Kharlamov
2021-05-17 19:51 ` PING " Konstantin Kharlamov
2021-05-19 17:28 ` Bjorn Helgaas
2021-05-19 19:12 ` Rafael J. Wysocki
2021-05-19 19:48 ` Bjorn Helgaas
2021-05-20 11:27 ` Rafael J. Wysocki
2021-05-20 11:54 ` Rafael J. Wysocki
2021-05-20 19:49 ` Bjorn Helgaas
2021-05-20 23:28 ` Konstantin Kharlamov [this message]
2021-05-24 6:59 ` Konstantin Kharlamov
2021-05-20 23:55 ` [PATCH v2] PCI: don't call firmware hooks on suspend unless it's fw-controlled Konstantin Kharlamov
2021-05-28 7:39 ` PING: " Konstantin Kharlamov
2021-06-03 8:36 ` PING: " Konstantin Kharlamov
2021-06-03 17:46 ` Bjorn Helgaas
2021-06-04 8:30 ` Konstantin Kharlamov
2021-05-21 9:47 ` [PATCH] PCI: don't power-off apple thunderbolt controller on s2idle Rafael J. Wysocki
2021-05-07 15:02 ` Rafael J. Wysocki
2021-05-08 8:20 ` Lukas Wunner
2021-05-07 9:32 ` Konstantin Kharlamov
2021-05-07 13:07 ` Bjorn Helgaas
2021-05-07 13:48 ` Konstantin Kharlamov
2021-05-20 11:58 ` Rafael J. Wysocki
2021-06-07 23:17 ` Bjorn Helgaas
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