Re: [RFC 2/3] PM: Don't pass up device_resume() -EBUSY errors

["Mario Limonciello (AMD) (kernel.org)" <superm1@kernel.org>]

On 10/20/2025 12:18 PM, Rafael J. Wysocki wrote:
> On Mon, Oct 20, 2025 at 6:53 PM Mario Limonciello (AMD)
> <superm1@kernel.org> wrote:
>>
>> From: Mario Limonciello <mario.limonciello@amd.com>
>>
>> If a device resume returns -EBUSY the device resume sequence has
>> been skipped.
> 
> Is this actually demonstrably true in all of the cases?
> 
> And what about -EAGAIN?
> 

I haven't audited codepaths of all drivers to guarantee it to be true 
for all cases.  That's the main reason I wanted to make it RFC - to 
discuss the idea of a dedicated return code to indicate it was skipped.

Another idea I had is that we could make it return a positive number, 
and PM core could recognize that as a skip.

So would like your thoughts against the ideas currently presented:

* -EAGAIN
* -EBUSY
* Some other return code
* > 0

Whichever is decided the PM core documentation would need to be updated 
to match as well.

>> Don't show errors for this or pass it up to async
>> resume.  If resume is run again in another stage the device should
>> try again.
>>
>> Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
>> Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>
>> ---
>>   drivers/base/power/main.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
>> index bf9c3d79c455f..f6bc7ef9a8371 100644
>> --- a/drivers/base/power/main.c
>> +++ b/drivers/base/power/main.c
>> @@ -1112,7 +1112,9 @@ static void device_resume(struct device *dev, pm_message_t state, bool async)
>>
>>          TRACE_RESUME(error);
>>
>> -       if (error) {
>> +       if (error == -EBUSY)
>> +               pm_dev_dbg(dev, state, async ? " async" : "");
>> +       else if (error) {
>>                  WRITE_ONCE(async_error, error);
>>                  dpm_save_failed_dev(dev_name(dev));
>>                  pm_dev_err(dev, state, async ? " async" : "", error);
>> --
>> 2.43.0
>>