From: Bjorn Helgaas <email@example.com>
To: "Rafael J. Wysocki" <firstname.lastname@example.org>
Cc: Konstantin Kharlamov <email@example.com>,
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: Wed, 19 May 2021 14:48:53 -0500 [thread overview]
Message-ID: <20210519194853.GA249712@bjorn-Precision-5520> (raw)
On Wed, May 19, 2021 at 09:12:26PM +0200, Rafael J. Wysocki wrote:
> On Wed, May 19, 2021 at 7:28 PM Bjorn Helgaas <email@example.com> wrote:
> > On Fri, May 07, 2021 at 05:08:42PM +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.
> > > > 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.
> > No, that's not my point at all. I don't really care whether the
> > interface is called pm_suspend_via_firmware() or is_s2idle().
> > What I don't like about this is that it's all just unexplained magic,
> > as was the original quirk.
> > IIUC, the quirk is applied by pci_pm_suspend_noirq() *after* it puts
> > the device in a low-power state. Here's my uninformed speculation
> > about what happens:
> > - On suspend, pci_pm_suspend_noirq() puts device in low-power state.
> > My *guess* is this means D0 or D3hot for s2idle, and D3cold for
> > everything else.
> This really depends on the ACPI methods involved, but as a rule (and
> I'm not aware of any exceptions) the target power state of the device
> for s2idle and "everything else" is the same. If D3cold is possible,
> it will be D3cold. If not, that will be D3hot etc.
> The only difference (from the individual device perspective) is that
> in the ACPI S3 (or S4 if this matters here) case the platform firmware
> (and that's not AML but something like SMM) may cut power off from it
> > [Do we have sufficient debug to find out what these states are?]
> I'm not sure what you mean. What states are supported or something else?
I was curious about what states we actually put this device in for
s2idle/standby/s2ram/std because I was hoping we could decide based
on what state s2idle used. But if they all use the same target state,
that idea won't work.
> > - pci_pm_suspend_noirq() does pci_fixup_suspend_late fixups,
> > including quirk_apple_poweroff_thunderbolt().
> > - quirk_apple_poweroff_thunderbolt() runs the magic SXIO/SXFP/SXLF
> > methods, which apparently turn off more power.
> > - On resume, pci_pm_resume_noirq() brings the device back to D0.
> > If we're resuming from standby, S2RAM, or STD, I speculate the
> > device is in D3cold, so this involves running AML that seems to
> > undo whatever SXIO/SXFP/SXLF did.
> The standby, S2RAM and STD cases are actually different in that respect.
> In the STD case we get the device from the restore kernel and it most
> likely has been enumerated by it, so it is in whatever power state the
> restore kernel puts it into.
> For standby that most likely is the state in which the device was left
> during suspend.
> For S2RAM, it most likely will be something like D0-uninitialized,
> because the platform firmware initiating the resume transition (which
> is not AML, but again something like SMM) restores power to the
> platform (including the majority of devices), but doesn't initialize
> them as a rule.
> The STD and S2RAM resume will undo the "magic", standby resume may not.
> > If we're resuming from s2idle, I speculate the device is in D0 or
> > D3hot, and we run different AML (or maybe no AML at all), and we
> It is in whatever power state it was left in during suspend and we run
> the same AML as in the other cases, modulo the possible power state
> difference (with respect to the other cases).
> > *don't* undo the effects of SXIO/SXFP/SXLF, so the device doesn't
> > work.
> This is correct.
> > If the above is anything like what's happening, we should be able to
> > skip SXIO/SXFP/SXLF based on the current power state of the device.
> Not really.
> > E.g., if the device is in D0 or D3hot, we should not use
> > SXIO/SXFP/SXLF to yank power.
> > That would seem more connected to the observable state of the device
> > than using pm_suspend_via_firmware(), which relies on the connection
> > between s2idle and PM_SUSPEND_FLAG_FW_SUSPEND (which is not at all
> > obvious) and the power state of the device while in s2idle (also not
> > obvious).
> 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. That makes it really
hard to figure out how this patch works and how to avoid breaking it
in the future.
Thanks for your patience in explaining all this!
next prev parent reply other threads:[~2021-05-19 19:48 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 [this message]
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
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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