Re: [PATCH] drm/vkms: Solve bug on kms_crc_cursor tests

[Shayenne Moura]

Em qui, 28 de fev de 2019 Ãs 11:03, Ville SyrjÃlÃ
<ville.syrjala@xxxxxxxxxxxxxxx> escreveu:
>
> On Thu, Feb 28, 2019 at 11:11:07AM +0100, Daniel Vetter wrote:
> > On Mon, Feb 25, 2019 at 11:26:06AM -0300, Shayenne Moura wrote:
> > > vkms_crc_work_handle needs the value of the actual frame to
> > > schedule the workqueue that calls periodically the vblank
> > > handler and the destroy state functions. However, the frame
> > > value returned from vkms_vblank_simulate is updated and
> > > diminished in vblank_get_timestamp because it is not in a
> > > vblank interrupt, and return an inaccurate value.
> > >
> > > Solve this getting the actual vblank frame directly from the
> > > vblank->count inside the `struct drm_crtc`, instead of using
> > > the `drm_accurate_vblank_count` function.
> > >
> > > Signed-off-by: Shayenne Moura <shayenneluzmoura@xxxxxxxxx>
> >
> > Sorry for the delay, I'm a bit swamped right now :-/
> >
> > Debug work you're doing here is really impressive! But I have no idea
> > what's going on. It doesn't look like it's just papering over a bug (like
> > the in_vblank_irq check we've discussed on irc), but I also have no idea
> > why it works.
> >
> > I'll pull in Ville, he understands this better than me.
>
> It's not entirely clear what we're trying to fix. From what I can see
> the crc work seems to be in no way synchronized with page flips, so
> I'm not sure how all this is really supposed to work.
>

Hi, Ville!

Thank you for the review! :)

I do not understand well what crc code is doing, but the issue that I found
is related to the vblank timestamp and frame count.

When vkms handles the crc_cursor it uses the start frame and end frame
values to verify if it needs to call the function 'drm_crtc_add_crc_entry()'
for each frame.

However, when getting the frame count, the code is calling the function
drm_update_vblank_count(dev, pipe, false) and, because of the 'false',
subtracting the actual vblank timestamp (consequently, the frame count
value), causing conflicts.

Does it make sense? I am not sure about this crc code behavior.

Shayenne

> > -Daniel
> >
> > > ---
> > >  drivers/gpu/drm/vkms/vkms_crc.c  | 4 +++-
> > >  drivers/gpu/drm/vkms/vkms_crtc.c | 4 +++-
> > >  2 files changed, 6 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/vkms/vkms_crc.c b/drivers/gpu/drm/vkms/vkms_crc.c
> > > index d7b409a3c0f8..09a8b00ef1f1 100644
> > > --- a/drivers/gpu/drm/vkms/vkms_crc.c
> > > +++ b/drivers/gpu/drm/vkms/vkms_crc.c
> > > @@ -161,6 +161,8 @@ void vkms_crc_work_handle(struct work_struct *work)
> > >     struct vkms_output *out = drm_crtc_to_vkms_output(crtc);
> > >     struct vkms_device *vdev = container_of(out, struct vkms_device,
> > >                                             output);
> > > +   unsigned int pipe = drm_crtc_index(crtc);
> > > +   struct drm_vblank_crtc *vblank = &crtc->dev->vblank[pipe];
> > >     struct vkms_crc_data *primary_crc = NULL;
> > >     struct vkms_crc_data *cursor_crc = NULL;
> > >     struct drm_plane *plane;
> > > @@ -196,7 +198,7 @@ void vkms_crc_work_handle(struct work_struct *work)
> > >     if (primary_crc)
> > >             crc32 = _vkms_get_crc(primary_crc, cursor_crc);
> > >
> > > -   frame_end = drm_crtc_accurate_vblank_count(crtc);
> > > +   frame_end = vblank->count;
> > >
> > >     /* queue_work can fail to schedule crc_work; add crc for
> > >      * missing frames
> > > diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c b/drivers/gpu/drm/vkms/vkms_crtc.c
> > > index 8a9aeb0a9ea8..9bf3268e2e92 100644
> > > --- a/drivers/gpu/drm/vkms/vkms_crtc.c
> > > +++ b/drivers/gpu/drm/vkms/vkms_crtc.c
> > > @@ -10,6 +10,8 @@ static enum hrtimer_restart vkms_vblank_simulate(struct hrtimer *timer)
> > >                                               vblank_hrtimer);
> > >     struct drm_crtc *crtc = &output->crtc;
> > >     struct vkms_crtc_state *state = to_vkms_crtc_state(crtc->state);
> > > +   unsigned int pipe = drm_crtc_index(crtc);
> > > +   struct drm_vblank_crtc *vblank = &crtc->dev->vblank[pipe];
> > >     u64 ret_overrun;
> > >     bool ret;
> > >
> > > @@ -20,7 +22,7 @@ static enum hrtimer_restart vkms_vblank_simulate(struct hrtimer *timer)
> > >             DRM_ERROR("vkms failure on handling vblank");
> > >
> > >     if (state && output->crc_enabled) {
> > > -           u64 frame = drm_crtc_accurate_vblank_count(crtc);
> > > +           u64 frame = vblank->count;
> > >
> > >             /* update frame_start only if a queued vkms_crc_work_handle()
> > >              * has read the data
> > > --
> > > 2.17.1
> > >
> >
> > --
> > Daniel Vetter
> > Software Engineer, Intel Corporation
> > http://blog.ffwll.ch
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@xxxxxxxxxxxxxxxxxxxxx
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
>
> --
> Ville SyrjÃlÃ
> Intel