On Thu, Sep 10, 2015 at 02:38:53PM -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. > Avoid the problem by making sure we don't return scanline_offset from > the get_crtc_scanline function. In moving the code there, I add to add > an additional delay since it could be called and have a legitimate 0 > result for some time (depending on the pixel clock). > > v2: move hsw dsl read hack to get_crtc_scanline (Ville) > > References: https://bugs.freedesktop.org/show_bug.cgi?id=91579 > Signed-off-by: Jesse Barnes <jbar...@virtuousgeek.org> > --- > drivers/gpu/drm/i915/i915_irq.c | 21 +++++++++++++++++++++ > 1 file changed, 21 insertions(+) > > diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c > index 90bc6c2..97e5d52 100644 > --- a/drivers/gpu/drm/i915/i915_irq.c > +++ b/drivers/gpu/drm/i915/i915_irq.c > @@ -697,6 +697,27 @@ static int __intel_get_crtc_scanline(struct intel_crtc > *crtc) > position = __raw_i915_read32(dev_priv, PIPEDSL(pipe)) & > DSL_LINEMASK_GEN3; > > /* > + * On HSW, the DSL reg (0x70000) appears to return 0 if we > + * read it right around the start of vblank. So try it again > + * so we don't accidentally end up spanning a vblank frame > + * increment, causing the pipe_update_end() code to squak at us. > + */ > + if (IS_HASWELL(dev) && !position) { > + int i, temp; > + > + for (i = 0; i < 100; i++) { > + udelay(1); > + temp = __raw_i915_read32(dev_priv, PIPEDSL(pipe)) & > + DSL_LINEMASK_GEN3; > + if (temp != position) { > + position = temp; > + goto out; > + } > + } > + }
Hmm. Another idea. If it always happens at start of vbl, maybe have a look at the ISR. If scanline reads 0, but ISR says we're in vblank, just return vblank_start. That's assming ISR would in fact show that it's in vblank when this happens. > + > +out: > + /* > * See update_scanline_offset() for the details on the > * scanline_offset adjustment. > */ > -- > 1.9.1 > > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@lists.freedesktop.org > http://lists.freedesktop.org/mailman/listinfo/intel-gfx -- Ville Syrjälä Intel OTC _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/intel-gfx
