linux-kernel - Re: [PATCH] drm/i915: Fix screen flickering on X

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Message-ID: <20150423091532.GA21511@nuc-i3427.alporthouse.com>
Date:	Thu, 23 Apr 2015 10:15:32 +0100
From:	Chris Wilson <chris@...is-wilson.co.uk>
To:	Matt Roper <matthew.d.roper@...el.com>
Cc:	linux-kernel@...r.kernel.org, intel-gfx@...ts.freedesktop.org
Subject: Re: [PATCH] drm/i915: Fix screen flickering on X

[cc'ing the authors]

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@...ev.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
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