[PATCH] drm: Schedule the output_poll_work with 1s delay if we have delayed event

[Peter Ujfalusi]

On 01/05/2017 10:43 AM, Daniel Vetter wrote:
> On Wed, Jan 04, 2017 at 02:00:53PM +0200, Peter Ujfalusi wrote:
>> Instead of scheduling the work to handle the initial delayed event, use 1s
>> delay.
>>
>> When the delayed event is handled w/o delay - in a similar matter when the
>> poll had been initialized before drm_helper_probe_single_connector_modes()
>> is called - it triggers a race in Optimus setups.
>>
>> Fixes: 339fd36238dd ("drm: drm_probe_helper: Fix output_poll_work scheduling")
>> Cc: stable at vger.kernel.org   # v4.9
>> Signed-off-by: Peter Ujfalusi <peter.ujfalusi at ti.com>
>> ---
>> Hi,
>>
>> related bug report: https://bugs.freedesktop.org/show_bug.cgi?id=98690
>>
>> Regards,
>> Peter
>>
>>  drivers/gpu/drm/drm_probe_helper.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
>> index 98ed110e28ed..f30c14b0a72f 100644
>> --- a/drivers/gpu/drm/drm_probe_helper.c
>> +++ b/drivers/gpu/drm/drm_probe_helper.c
>> @@ -146,8 +146,9 @@ void drm_kms_helper_poll_enable_locked(struct drm_device *dev)
>>  	drm_connector_list_iter_put(&conn_iter);
>>  
>>  	if (dev->mode_config.delayed_event) {
>> +		/* Use short (1s) delay to handle the initial delayed event */
>>  		poll = true;
>> -		delay = 0;
>> +		delay = HZ;
> 
> This smells a bit like duct-tape papering over some other race.

Yes, I agree. We could revert 339fd36238dd also to put back the duct-tape.

> Lack of
> locking or something else. Most likely some drivers enable polling a bit
> too early in their load sequence.

All is pointing to Optimus. Intel and nouveau alone works, but we have
failure on Optimus laptops.
I have tried to narrow it down with another patch attached to the
bugzilla: https://bugs.freedesktop.org/attachment.cgi?id=128742

I expected it to fix the problem. But it did not. So I'm puzzled.

>And if we can't figure this out, then we
> need some really big FIXME: here that this papers over driver races.

Yeah, now we know that there is something wrong in some driver(s). We
can hide it with delaying the poll_work. It would be great if
nouveau/optimus guys would be able to take a look at this.

> -Daniel
> 
>>  	}
>>  
>>  	if (poll)
>> -- 
>> 2.11.0
>>
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> 

-- 
Péter