[Intel-gfx] [PATCH] drm/i915: Fix screen flickering on X

[Matt Roper]

On Thu, May 07, 2015 at 12:12:18PM +0300, Jani Nikula wrote:
> On Thu, 23 Apr 2015, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> > [cc'ing the authors]
> 
> This has been posted earlier [1] and it has review to be addressed [2].
> 
> BR,
> Jani.

I agree with Ander's response in [2]...we can't call
intel_update_watermarks() in the commit function because we're under
vblank evasion.  We should already be flagging the transaction as
needing a watermark update in intel_check_cursor_plane(), and that flag
will be acted upon immediately after the commit functions are done
running, once we've re-enabled interrupts.

Note that our current codebase looks a bit different since we've dropped
intel_crtc->cursor_{width,height}.  So the relevant check in
intel_check_cursor_plane() now looks like:

        if (plane->state->crtc_w != state->base.crtc_w)
                intel_crtc->atomic.update_wm = true;

Is there a bugzilla open on this issue with more details?


Matt

> 
> 
> [1] http://mid.gmane.org/1428790644-6812-1-git-send-email-ismael@iodev.co.uk
> [2] http://mid.gmane.org/1428928418.2654.8.camel@gmail.com
> 
> 
> >
> > On Sat, Apr 11, 2015 at 07:40:34PM -0300, Ismael Luceno wrote:
> >> A bisect showed that commit 32b7eeec4d1e861230b09d437e95d76c86ff4a68
> >> introduced the issue.
> >> 
> >> The issue starts as soon as X takes control of the screen, even if just
> >> a plain X doing nothing, so based on the code touched by the commit I
> >> thought it had to be related to the so called "hardware cursor". I
> >> confirmed it when hiding the cursor made the flickering go away.
> >> 
> >> The aforementioned commit removed some suspicious code, and the
> >> Programmer's Reference Manual confirmed my suspicion:
> >> 
> >> "Incorrectly programmed watermark values can result in screen corruption.
> >> 
> >> The watermarks should be calculated and programmed when any of the
> >> watermark calculation inputs change. This includes planes enabling or
> >> disabling, plane source format or size changing, etc."
> >> 
> >> So I'm re-adding the few lines that update the watermarks after a cursor
> >> size change.
> >> 
> >> Signed-off-by: Ismael Luceno <ismael at iodev.co.uk>
> >> ---
> >>  drivers/gpu/drm/i915/intel_display.c | 7 ++++++-
> >>  1 file changed, 6 insertions(+), 1 deletion(-)
> >> 
> >> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> >> index f75173c..e23f062 100644
> >> --- a/drivers/gpu/drm/i915/intel_display.c
> >> +++ b/drivers/gpu/drm/i915/intel_display.c
> >> @@ -12258,6 +12258,7 @@ intel_commit_cursor_plane(struct drm_plane *plane,
> >>  	struct intel_crtc *intel_crtc;
> >>  	struct intel_plane *intel_plane = to_intel_plane(plane);
> >>  	struct drm_i915_gem_object *obj = intel_fb_obj(state->base.fb);
> >> +	unsigned old_width;
> >>  	uint32_t addr;
> >>  
> >>  	crtc = crtc ? crtc : plane->crtc;
> >> @@ -12282,11 +12283,15 @@ intel_commit_cursor_plane(struct drm_plane *plane,
> >>  	intel_crtc->cursor_addr = addr;
> >>  	intel_crtc->cursor_bo = obj;
> >>  update:
> >> +	old_width = intel_crtc->cursor_width;
> >>  	intel_crtc->cursor_width = state->base.crtc_w;
> >>  	intel_crtc->cursor_height = state->base.crtc_h;
> >>  
> >> -	if (intel_crtc->active)
> >> +	if (intel_crtc->active) {
> >> +		if (old_width != intel_crtc->cursor_width)
> >> +			intel_update_watermarks(crtc);
> >>  		intel_crtc_update_cursor(crtc, state->visible);
> >> +	}
> >>  }
> >>  
> >>  static struct drm_plane *intel_cursor_plane_create(struct drm_device *dev,
> >> -- 
> >> 2.3.4
> >
> > -- 
> > Chris Wilson, Intel Open Source Technology Centre
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> -- 
> Jani Nikula, Intel Open Source Technology Center

-- 
Matt Roper
Graphics Software Engineer
IoTG Platform Enabling & Development
Intel Corporation
(916) 356-2795