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

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Date:   Tue, 5 Nov 2019 05:08:04 -0500
From:   Brian Masney <masneyb@...tation.org>
To:     Rob Clark <robdclark@...il.com>
Cc:     Rob Clark <robdclark@...omium.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Sean Paul <sean@...rly.run>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>
Subject: Re: [Freedreno] drm/msm: 'pp done time out' errors after async
 commit changes

On Mon, Nov 04, 2019 at 04:19:07PM -0800, Rob Clark wrote:
> On Mon, Nov 4, 2019 at 4:01 PM Brian Masney <masneyb@...tation.org> wrote:
> >
> > Hey Rob,
> >
> > Since commit 2d99ced787e3 ("drm/msm: async commit support"), the frame
> > buffer console on my Nexus 5 began throwing these errors:
> >
> > msm fd900000.mdss: pp done time out, lm=0
> >
> > The display still works.
> >
> > I see that mdp5_flush_commit() was introduced in commit 9f6b65642bd2
> > ("drm/msm: add kms->flush_commit()") with a TODO comment and the commit
> > description mentions flushing registers. I assume that this is the
> > proper fix. If so, can you point me to where these registers are
> > defined and I can work on the mdp5 implementation.
> 
> See mdp5_ctl_commit(), which writes the CTL_FLUSH registers.. the idea
> would be to defer writing CTL_FLUSH[ctl_id] = flush_mask until
> kms->flush() (which happens from a timer shortly before vblank).
> 
> But I think the async flush case should not come up with fbcon?  It
> was really added to cope with hwcursor updates (and userspace that
> assumes it can do an unlimited # of cursor updates per frame).. the
> intention was that nothing should change in the sequence for mdp5 (but
> I guess that was not the case).

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.

Brian