[PATCH 03/17] drm: convert crtc and mode_config to ww_mutex

[Rob Clark]

On Mon, May 26, 2014 at 4:23 AM, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Sun, May 25, 2014 at 07:16:43PM -0400, Rob Clark wrote:
>> On Sun, May 25, 2014 at 6:10 PM, Daniel Vetter <daniel at ffwll.ch> wrote:
>> > On Sat, May 24, 2014 at 8:30 PM, Rob Clark <robdclark at gmail.com> wrote:
>> >> @@ -8002,7 +8002,7 @@ bool intel_get_load_detect_pipe(struct drm_connector *connector,
>> >>         if (encoder->crtc) {
>> >>                 crtc = encoder->crtc;
>> >>
>> >> -               mutex_lock(&crtc->mutex);
>> >> +               drm_modeset_lock(&crtc->mutex, NULL);
>> >
>> >
>> > This is pretty much the reason why I think switching the
>> > mode_config.mutex to a ww_mutex is a bad idea: This call here nests
>> > within the mode_config.mutex and so must be acquired. Wiring the
>> > acquire context through everything is going to be fairly horrible,
>> > especially since you must be able to bail out when trying to lock with
>> > an axquire context.
>>
>> which is the call-path to here from mode_config.mutex?  Is it possible
>> to just move the locking to a higher level for a
>> drm_modeset_lock_all()?
>
> Connector probing. And the entire point of crtc locks was to _not_ block
> all screen updates while we poke for a new edid or do load balancing. If
> you want to test this you need a gen3/4 with tv-out (native, not through
> sdvo) or a gen2 or i915g/gm with vga.


hmm, I guess I'm still not quite seeing the issue.  For non-atomic
paths, we are grabbing mode_config and/or crtc mutex as bare mutexes
in same spots as we did before.  So if it worked before without
nested_lock stuff it should still work now.

BR,
-R