[Freedreno] drm/msm: 'pp done time out' errors after async commit changes

[Rob Clark]

On Wed, Nov 6, 2019 at 1:13 AM Brian Masney <masneyb at onstation.org> wrote:
>
> On Tue, Nov 05, 2019 at 08:23:27AM -0800, Rob Clark wrote:
> > On Tue, Nov 5, 2019 at 2:08 AM Brian Masney <masneyb at onstation.org> wrote:
> > > The 'pp done time out' errors go away if I revert the following three
> > > commits:
> > >
> > > cd6d923167b1 ("drm/msm/dpu: async commit support")
> > > d934a712c5e6 ("drm/msm: add atomic traces")
> > > 2d99ced787e3 ("drm/msm: async commit support")
> > >
> > > I reverted the first one to fix a compiler error, and the second one so
> > > that the last patch can be reverted without any merge conflicts.
> > >
> > > I see that crtc_flush() calls mdp5_ctl_commit(). I tried to use
> > > crtc_flush_all() in mdp5_flush_commit() and the contents of the frame
> > > buffer dance around the screen like its out of sync. I renamed
> > > crtc_flush_all() to mdp5_crtc_flush_all() and removed the static
> > > declaration. Here's the relevant part of what I tried:
> > >
> > > --- a/drivers/gpu/drm/msm/disp/mdp5/mdp5_kms.c
> > > +++ b/drivers/gpu/drm/msm/disp/mdp5/mdp5_kms.c
> > > @@ -171,7 +171,15 @@ static void mdp5_prepare_commit(struct msm_kms *kms, struct drm_atomic_state *st
> > >
> > >  static void mdp5_flush_commit(struct msm_kms *kms, unsigned crtc_mask)
> > >  {
> > > -       /* TODO */
> > > +       struct mdp5_kms *mdp5_kms = to_mdp5_kms(to_mdp_kms(kms));
> > > +       struct drm_crtc *crtc;
> > > +
> > > +       for_each_crtc_mask(mdp5_kms->dev, crtc, crtc_mask) {
> > > +               if (!crtc->state->active)
> > > +                       continue;
> > > +
> > > +               mdp5_crtc_flush_all(crtc);
> > > +       }
> > >  }
> > >
> > > Any tips would be appreciated.
> >
> >
> > I think this is along the lines of what we need to enable async commit
> > for mdp5 (but also removing the flush from the atomic-commit path)..
> > the principle behind the async commit is to do all the atomic state
> > commit normally, but defer writing the flush bits.  This way, if you
> > get another async update before the next vblank, you just apply it
> > immediately instead of waiting for vblank.
> >
> > But I guess you are on a command mode panel, if I remember?  Which is
> > a case I didn't have a way to test.  And I'm not entirely about how
> > kms_funcs->vsync_time() should be implemented for cmd mode panels.
>
> Yes, this is a command-mode panel and there's no hardware frame counter
> available. The key to getting the display working on this phone was this
> patch:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=2bab52af6fe68c43b327a57e5ce5fc10eefdfadf
>
> > That all said, I think we should first fix what is broken, before
> > worrying about extending async commit support to mdp5.. which
> > shouldn't hit the async==true path, due to not implementing
> > kms_funcs->vsync_time().
> >
> > What I think is going on is that, in the cmd mode case,
> > mdp5_wait_flush() (indirectly) calls mdp5_crtc_wait_for_pp_done(),
> > which waits for a pp-done irq regardless of whether there is a flush
> > in progress.  Since there is no flush pending, the irq never comes.
> > But the expectation is that kms_funcs->wait_flush() returns
> > immediately if there is nothing to wait for.
>
> I don't think that's happening in this case. I added some pr_info()
> statements to request_pp_done_pending() and mdp5_crtc_pp_done_irq().
> Here's the first two sets of messages that appear in dmesg:
>
> [   14.018907] msm fd900000.mdss: pp done time out, lm=0
> [   14.018993] request_pp_done_pending: HERE
> [   14.074208] mdp5_crtc_pp_done_irq: HERE
> [   14.074368] Console: switching to colour frame buffer device 135x120
> [   14.138938] msm fd900000.mdss: pp done time out, lm=0
> [   14.139021] request_pp_done_pending: HERE
> [   14.158097] mdp5_crtc_pp_done_irq: HERE
>
> The messages go on like this with the same pattern.
>
> I tried two different changes:
>
> 1) I moved the request_pp_done_pending() and corresponding if statement
>    from mdp5_crtc_atomic_flush() and into mdp5_crtc_atomic_begin().
>
> 2) I increased the timeout in wait_for_completion_timeout() by several
>    increments; all the way to 5 seconds.

increasing the timeout won't help, because the pp-done irq has already
come at the point where we wait for it..

maybe the easy thing is just add mdp5_crtc->needs_pp, set to true
before requesting, and false when we get the irq.. and then
mdp5_crtc_wait_for_pp_done() just returns if needs_pp==false..

BR,
-R

> I haven't dug into the new code anymore.
>
> Brian