On 04/20/2017 01:33 PM, Rafael J. Wysocki wrote:
On Thu, Apr 20, 2017 at 9:25 AM, Jarkko Nikula
<jarkko.nikula@xxxxxxxxxxxxxxx> wrote:
Hi
On 04/19/2017 11:24 PM, Rafael J. Wysocki wrote:
On Thu, Mar 30, 2017 at 2:04 PM, Jarkko Nikula
<jarkko.nikula@xxxxxxxxxxxxxxx> wrote:
There is possibility to enter dw_i2c_plat_suspend() callback twice
during system suspend under certain cases which is causing here warnings
from clk_core_disable() and clk_core_unprepare() as well as accessing the
registers that can be power gated.
Commit 8503ff166504 ("i2c: designware: Avoid unnecessary resuming during
system suspend") implemented a prepare callback that checks for runtime
suspended device which allow PM core to set direct_complete flag and
skip system suspend and resume callbacks.
However it can still happen if nothing resumes the device prior system
syspend (e.g. acpi_subsys_suspend()) and there is a slave device which
unsets the direct_complete flag of the parent in __device_suspend() thus
causing PM code to not skip the system suspend/resume callbacks.
Avoid this by checking runtime status in suspend and resume callbacks
and return directly if device is runtime suspended. This affects only
system suspend/resume since during runtime suspend/resume runtime status
is suspending (not suspended) or resuming.
Signed-off-by: Jarkko Nikula <jarkko.nikula@xxxxxxxxxxxxxxx>
---
I'm able to trigger system suspend callback while device is runtime
suspended by removing the pm_runtime_resume() call from
drivers/mfd/intel-lpss.c: resume_lpss_device() and having unbound I2C
slave (ACPI enumerated but doesn't bind due an error in probe function).
In that case __device_suspend() for that unbound device has NULL suspend
callback, and thus doesn't cause any runtime resume chain but still
unsets
the parent's direct_complete flag.
John Stult <john.stultz@xxxxxxxxxx> has reported he can trigger this on
HiKey board too.
I'm not sure is this the right thing to do. It feels something the PM
core
should do but I'm not sure that either. One alternative could be to
resume
runtime suspended parent in in __device_suspend() right after where
parent's direct_complete flag is unset.
In that case the core expects that the ->prepare callback for the
slave will also return 1 (or a positive number in general).
If that doesn't happen, then from the core's perspective it is not
safe to allow the master's system PM callbacks to be skipped and
that's why direct_complete is unset for it.
So it's then right thing to check runtime PM status in driver as patch does
below?
If you know for a fact that none of the device's children and none of
the children thereof and so on and nothing that may depend on the
device via a device_link, either directly or indirectly, will ever
need to be resumed during system suspend, then yes, it is.
Otherwise, no, it isn't.
If you were wondering the pm_runtime_suspended() check in
dw_i2c_plat_resume() that too was for skipping double callback by system
resume followed by later runtime resume leading to ever increasing clock
enable count over repeated system suspend/resume cycles.
Anyway, normal case here is we do runtime resume during system suspend
from a few places. E.g. ACPI enumerated slave does suspend through
acpi_subsys_suspend() chain and for Intel platforms i2c-designware is
resumer either from drivers/acpi/acpi_lpss.c or drivers/mfd/intel-lpss.c.
If we are doing expected suspend/resume callback then our runtime_status
is other than RPM_SUSPENDED and pm_runtime_suspended() returns false.
--
Jarkko
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