On Thu, Sep 10, 2015 at 08:34:22AM -0700, Jesse Barnes wrote: > On HSW at least (still testing other platforms, but should be harmless > elsewhere), the DSL reg reads back as 0 when read around vblank start > time. This ends up confusing the atomic start/end checking code, since > it causes the update to appear as if it crossed a frame count boundary. > Workaround that by avoiding updates in the first couple of scanlines. > In testing, even a delay of a single microsecond is enough to give us a > good DSL value again, so the millisecond we'll wait when we hit this > case occasionally ought to be plenty. > > References: https://bugs.freedesktop.org/show_bug.cgi?id=91579 > Signed-off-by: Jesse Barnes <jbarnes@xxxxxxxxxxxxxxxx> > --- > drivers/gpu/drm/i915/intel_sprite.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/intel_sprite.c b/drivers/gpu/drm/i915/intel_sprite.c > index ca7e264..0c2c62f 100644 > --- a/drivers/gpu/drm/i915/intel_sprite.c > +++ b/drivers/gpu/drm/i915/intel_sprite.c > @@ -113,8 +113,16 @@ void intel_pipe_update_start(struct intel_crtc *crtc) > */ > prepare_to_wait(wq, &wait, TASK_UNINTERRUPTIBLE); > > + /* > + * On HSW, the DSL reg (0x70000) appears to return 0 if we > + * read it right around the start of vblank. So skip past it > + * so we don't accidentally end up spanning a vblank frame > + * increment, causing the update_end() code to squak at us. > + * (We use 2 in the comparison to account for the > + * scanline_offset used to correct the DSL readout.) > + */ > scanline = intel_get_crtc_scanline(crtc); > - if (scanline < min || scanline > max) > + if (scanline > 2 && (scanline < min || scanline > max)) > break; And it means we'll miss a frame whenever the scanline is 0-2 even on a non-broken. So I don't kike it. Dunno maybe something more targeted like: read dsl if (IS_HASWELL && scanline == crtc->scanline_offset) { udelay(1); read dsl again } in __intel_get_crtc_scanline()? The udelay() is a bit unfortunate, but we'll need accurate scanline informnation for the vblank timestamps too. > > if (timeout <= 0) { > -- > 1.9.1 > > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@xxxxxxxxxxxxxxxxxxxxx > http://lists.freedesktop.org/mailman/listinfo/intel-gfx -- Ville Syrjälä Intel OTC _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
