[PATCH] PM / Runtime: Defer resuming of the device in pm_runtime_force_resume()

[Ulf Hansson]

On 21 April 2016 at 21:23, Rafael J. Wysocki <rjw at rjwysocki.net> wrote:
> On Thursday, April 21, 2016 12:34:02 PM Ulf Hansson wrote:
>> When the pm_runtime_force_suspend|resume() helpers were invented, we still
>> had CONFIG_PM_RUNTIME and CONFIG_PM_SLEEP as separate Kconfig options.
>>
>> To make sure these helpers worked for all combinations and without
>> introducing too much of complexity, the device was always resumed in
>> pm_runtime_force_resume().
>>
>> More precisely, when CONFIG_PM_SLEEP was set and CONFIG_PM_RUNTIME was
>> unset, we needed to resume the device as the subsystem/driver couldn't
>> rely on using runtime PM to do it.
>>
>> As the CONFIG_PM_RUNTIME option was merged into CONFIG_PM a while ago, it
>> removed this combination, of using CONFIG_PM_SLEEP without the earlier
>> CONFIG_PM_RUNTIME.
>>
>> For this reason we can now rely on the subsystem/driver to use runtime PM
>> to resume the device, instead of forcing that to be done in all cases. In
>> other words, let's defer this to a later point when it's actually needed.
>>
>> Signed-off-by: Ulf Hansson <ulf.hansson at linaro.org>
>> ---
>>
>> Note, this patch is based upon another not yet queued patch [1]. The reason is
>> simply because that [1] is a more important patch as it fixes a problem. It was
>> posted to linux-pm April 8th and I expect it (or a new revision of it) to be
>> applied before $subject patch.
>>
>> [1]
>> https://patchwork.kernel.org/patch/8782851
>>
>> ---
>>  drivers/base/power/runtime.c | 11 +++++++++++
>>  1 file changed, 11 insertions(+)
>>
>> diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
>> index b746904..a190ca0 100644
>> --- a/drivers/base/power/runtime.c
>> +++ b/drivers/base/power/runtime.c
>> @@ -1506,6 +1506,17 @@ int pm_runtime_force_resume(struct device *dev)
>>               goto out;
>>       }
>>
>> +     /*
>> +      * The PM core increases the runtime PM usage count in the system PM
>> +      * prepare phase. If the count is greather than 1 at this point, someone
>> +      * else has also increased it. In such case, let's make sure to runtime
>> +      * resume the device as that is likely what is expected. In other case
>
> That doesn't sound quite right.  I'd rather say "In that case, invoke the
> runtime resume callback for the device as that is likely what is expected" here.

I definitely agree, let me send a respin in a while.

Besides this, I assume you are happy with the approach?

>
>> +      * we trust the subsystem/driver to runtime resume the device when it's
>> +      * actually needed.
>> +      */
>> +     if (atomic_read(&dev->power.usage_count) < 2)
>> +             goto out;
>> +
>>       ret = pm_runtime_set_active(dev);
>>       if (ret)
>>               goto out;
>>
>
> Thanks,
> Rafael
>

Kind regards
Uffe