linux-kernel - Re: [PATCH v2] PCI: PM: Skip devices in D0 for suspend-to-idle

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Message-ID: <f233d8fe-9525-05de-858d-e7456a17bd4b@nvidia.com>
Date:   Tue, 25 Jun 2019 13:46:40 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
CC:     Linux PCI <linux-pci@...r.kernel.org>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Keith Busch <kbusch@...nel.org>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        linux-tegra <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v2] PCI: PM: Skip devices in D0 for suspend-to-idle


On 25/06/2019 00:09, Rafael J. Wysocki wrote:
> On Tuesday, June 25, 2019 12:20:26 AM CEST Rafael J. Wysocki wrote:
>> On Mon, Jun 24, 2019 at 11:37 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>>>
>>> On Mon, Jun 24, 2019 at 2:43 PM Jon Hunter <jonathanh@...dia.com> wrote:
>>>>
>>>> Hi Rafael,
>>>>
>>>> On 13/06/2019 22:59, Rafael J. Wysocki wrote:
>>>>> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>>>>
>>>>> Commit d491f2b75237 ("PCI: PM: Avoid possible suspend-to-idle issue")
>>>>> attempted to avoid a problem with devices whose drivers want them to
>>>>> stay in D0 over suspend-to-idle and resume, but it did not go as far
>>>>> as it should with that.
>>>>>
>>>>> Namely, first of all, the power state of a PCI bridge with a
>>>>> downstream device in D0 must be D0 (based on the PCI PM spec r1.2,
>>>>> sec 6, table 6-1, if the bridge is not in D0, there can be no PCI
>>>>> transactions on its secondary bus), but that is not actively enforced
>>>>> during system-wide PM transitions, so use the skip_bus_pm flag
>>>>> introduced by commit d491f2b75237 for that.
>>>>>
>>>>> Second, the configuration of devices left in D0 (whatever the reason)
>>>>> during suspend-to-idle need not be changed and attempting to put them
>>>>> into D0 again by force is pointless, so explicitly avoid doing that.
>>>>>
>>>>> Fixes: d491f2b75237 ("PCI: PM: Avoid possible suspend-to-idle issue")
>>>>> Reported-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
>>>>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>>>> Reviewed-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
>>>>> Tested-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
>>>>
>>>> I have noticed a regression in both the mainline and -next branches on
>>>> one of our boards when testing suspend. The bisect is point to this
>>>> commit and reverting on top of mainline does fix the problem. So far I
>>>> have not looked at this in close detail but kernel log is showing ...
>>>
>>> Can you please collect a log like that, but with dynamic debug in
>>> pci-driver.c enabled?
>>>
>>> Note that reverting this commit is rather out of the question, so we
>>> need to get to the bottom of the failure.
>>
>> I suspect that there is a problem with the pm_suspend_via_firmware()
>> check which returns 'false' on the affected board, but the platform
>> actually removes power from devices left in D0 during suspend.
>>
>> I guess it would be more appropriate to check something like
>> pm_suspend_no_platform() which would return 'true' in the
>> suspend-to-idle patch w/ ACPI.
> 
> So I wonder if the patch below makes any difference?

Thanks. I will try this now and let you know.

Cheers!
Jon

-- 
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