linux-kernel - [PATCH v2] PM: sleep: core: Avoid setting power.must

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Date:   Tue, 10 Aug 2021 06:54:17 -0700
From:   Prasad Sodagudi <psodagud@...eaurora.org>
To:     gregkh@...uxfoundation.org, rjw@...ysocki.net
Cc:     len.brown@...el.com, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, pavel@....cz, psodagud@...eaurora.org
Subject: [PATCH v2] PM: sleep: core: Avoid setting power.must_resume to false

This is regarding suspend/resume(s2idle) scenario of devices and difference
between the LTS kernels 5.4 and 5.10 with respect to devices suspend and
resume. Observing that devices suspended in suspend_late stage are not
getting resumed in resume_early stage.
1) LTS kernel 5.4 kernel do not have this problem but 5.10 kernel
shows this problem.
2) 'commit 6e176bf8d461 ("PM: sleep: core: Do not skip callbacks in the resume phase")'
is skipping the driver early_resume callbacks.

In device_resume_early function dev->power.must_resume is used to skip the
resume call back. It looks this function is expecting that,
__device_suspend_noirq() would set dev->power.must_resume = true for the
devices which does not have DPM_FLAG_MAY_SKIP_RESUME flag set.

3) Problematic scenario is as follows -  During the device suspend/resume
scenario all the devices in  the suspend_late stage are successful and some
device can fail to suspend in suspend_noirq(device_suspend_noirq->
__device_suspend_noirq) phase.
As a device failed in dpm_noirq_suspend_devices phase, dpm_resume_noirq is
getting called to resume devices in dpm_late_early_list in the noirq phase.

4) During the Devices_early_resume stage
dpm_resume_early()-->device_resume_early() functions skipping the devices
early resume callbacks.
799         if (dev_pm_skip_resume(dev))
800                  goto Skip;

5) Devices suspended in suspend_late stage are not getting resumed in
Devices_early_resume stage because of
'commit 6e176bf8d461 ("PM: sleep: core: Do not skip callbacks in the resume phase")'
is skipping the driver early_resume callbacks when dev->power.must_resume is false.

Changelog:
v1 -> v2:
 - Fixed indentation comments.
 - Commit text updated to include scenario.

Prasad Sodagudi (1):
  PM: sleep: core: Avoid setting power.must_resume to false

 drivers/base/power/main.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

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