On Wed, Nov 21, 2018 at 5:16 PM Ville Syrjälä
<ville.syrjala@xxxxxxxxxxxxxxx> wrote:
>
> On Wed, Nov 21, 2018 at 04:19:36PM +0100, Daniel Vetter wrote:
> > On Wed, Nov 21, 2018 at 01:37:51PM +0200, Ville Syrjälä wrote:
> > > On Wed, Nov 21, 2018 at 10:27:27AM +0100, Daniel Vetter wrote:
> > > > On Mon, Nov 12, 2018 at 06:59:45PM +0200, Ville Syrjala wrote:
> > > > > From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> > > > >
> > > > > On i965gm we need to adjust max_vblank_count dynamically
> > > > > depending on whether the TV encoder is used or not. To
> > > > > that end add a per-crtc max_vblank_count that takes
> > > > > precedence over its device wide counterpart. The driver
> > > > > can now call drm_crtc_set_max_vblank_count() to configure
> > > > > the per-crtc value before calling drm_vblank_on().
> > > > >
> > > > > Also looks like there was some discussion about exynos needing
> > > > > similar treatment.
> > > > >
> > > > > Cc: stable@xxxxxxxxxxxxxxx
> > > > > Cc: Inki Dae <inki.dae@xxxxxxxxxxx>
> > > > > Cc: Daniel Vetter <daniel@xxxxxxxx>
> > > > > Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> > > > > ---
> > > > > drivers/gpu/drm/drm_vblank.c | 39 ++++++++++++++++++++++++++++++++----
> > > > > include/drm/drm_vblank.h | 8 ++++++++
> > > > > 2 files changed, 43 insertions(+), 4 deletions(-)
> > > > >
> > > > > diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> > > > > index 98e091175921..c3abbdca8aba 100644
> > > > > --- a/drivers/gpu/drm/drm_vblank.c
> > > > > +++ b/drivers/gpu/drm/drm_vblank.c
> > > > > @@ -105,13 +105,20 @@ static void store_vblank(struct drm_device *dev, unsigned int pipe,
> > > > > write_sequnlock(&vblank->seqlock);
> > > > > }
> > > > >
> > > > > +static u32 drm_max_vblank_count(struct drm_device *dev, unsigned int pipe)
> > > > > +{
> > > > > + struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
> > > > > +
> > > > > + return vblank->max_vblank_count ?: dev->max_vblank_count;
> > > > > +}
> > > > > +
> > > > > /*
> > > > > * "No hw counter" fallback implementation of .get_vblank_counter() hook,
> > > > > * if there is no useable hardware frame counter available.
> > > > > */
> > > > > static u32 drm_vblank_no_hw_counter(struct drm_device *dev, unsigned int pipe)
> > > > > {
> > > > > - WARN_ON_ONCE(dev->max_vblank_count != 0);
> > > > > + WARN_ON_ONCE(drm_max_vblank_count(dev, pipe) != 0);
> > > > > return 0;
> > > > > }
> > > > >
> > > > > @@ -198,6 +205,7 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> > > > > ktime_t t_vblank;
> > > > > int count = DRM_TIMESTAMP_MAXRETRIES;
> > > > > int framedur_ns = vblank->framedur_ns;
> > > > > + u32 max_vblank_count = drm_max_vblank_count(dev, pipe);
> > > > >
> > > > > /*
> > > > > * Interrupts were disabled prior to this call, so deal with counter
> > > > > @@ -216,9 +224,9 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> > > > > rc = drm_get_last_vbltimestamp(dev, pipe, &t_vblank, in_vblank_irq);
> > > > > } while (cur_vblank != __get_vblank_counter(dev, pipe) && --count > 0);
> > > > >
> > > > > - if (dev->max_vblank_count != 0) {
> > > > > + if (max_vblank_count) {
> > > > > /* trust the hw counter when it's around */
> > > > > - diff = (cur_vblank - vblank->last) & dev->max_vblank_count;
> > > > > + diff = (cur_vblank - vblank->last) & max_vblank_count;
> > > > > } else if (rc && framedur_ns) {
> > > > > u64 diff_ns = ktime_to_ns(ktime_sub(t_vblank, vblank->time));
> > > > >
> > > > > @@ -258,7 +266,8 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> > > > > pipe, vblank->count, diff, cur_vblank, vblank->last);
> > > > >
> > > > > if (diff == 0) {
> > > > > - WARN_ON_ONCE(cur_vblank != vblank->last);
> > > > > + WARN_ON_ONCE(max_vblank_count &&
> > > > > + cur_vblank != vblank->last);
> > > >
> > > > Unrelated bugfix for this warning? Should be a separate patch I think, or
> > > > I'm missing something.
> > >
> > > Ah, yeah this was due to a quirk of i965gm hardware. The hw counter
> > > does work until the exact point when we enable TV encoder. Thus we
> > > will get non-zero values up to that point, and since the TV encoder
> > > isn't yet throttling the pipe it presumably runs at the oversample
> > > clock so our timestamp based estimates can give us a diff==0 even
> > > though the pipe did indeed pass a vblank already. I forgot to
> > > note this in the commit message.
> > >
> > > I think we can handle this three ways:
> > > 1. do what I do here and just let the mismatch slip through
> > > 2. force i915_get_vblank_counter() to return 0 always when the
> > > TV encoder is going to be used
> > > 3. don't call drm_crtc_set_max_vblank_count() before drm_vblank_on()
> > > and instead delay it until just before we enable the TV encoder
> > >
> > > I think option 3 is overly complicated to consider seriously. So
> > > option 1 or option 2 is what I think we should do. For whatever
> > > reason I went with option 1 here, but maybe option 2 is better
> > > since it would be all contained within i915...
> >
> > Delay drm_crtc_vblank_on until the vblank is stable? That seems like the
> > semantically clean solution to me, instead of hacking around in core code
> > when drivers leak garbage out ...
>
> We need a vblank wait before turning on the TV encoder. Chicken vs. egg.
Gah.
Ok I think I think having the hack here makes sense then, but split
out as a separate patch with separate justification. It's a bit a
tricky thing that deserves to be higlighted (and easier way to found
the explanation with git blame in case it's ever needed).
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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