Re: [PATCH 2/2] drm/i915: Recompute WM when the cursor size changes

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Mar 26, 2014 at 12:38:15PM +0000, Chris Wilson wrote:
> If the cursor width is changed, we may need to recompute our WM to
> prevent untold flickering. We hope that the registers are flushed on the
> same vblank to prevent underruns...
> 
> Cc: Damien Lespiau <damien.lespiau@intel.com>
> Cc: Sagar Kamble <sagar.a.kamble@intel.com>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index c8c52d105b8c..e15b3abe1350 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -7763,6 +7763,7 @@ static int intel_crtc_cursor_set(struct drm_crtc *crtc,
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
>  	struct drm_i915_gem_object *obj;
> +	unsigned old_width;
>  	uint32_t addr;
>  	int ret;
>  
> @@ -7853,13 +7854,18 @@ static int intel_crtc_cursor_set(struct drm_crtc *crtc,
>  
>  	mutex_unlock(&dev->struct_mutex);
>  
> +	old_width = intel_crtc->cursor_width;
> +
>  	intel_crtc->cursor_addr = addr;
>  	intel_crtc->cursor_bo = obj;
>  	intel_crtc->cursor_width = width;
>  	intel_crtc->cursor_height = height;
>  
> -	if (intel_crtc->active)
> +	if (intel_crtc->active) {
> +		if (old_width != width)
> +			intel_update_watermarks(crtc);

Shouldn't we recompute when shrinking after and when growing before we
change the cursor size? vblank-syncing maybe even. Given all the amotic
foo we currently have I expect that cursors are as underrun prone as all
the other stuff is, too.

But can be done in a later patch, together with the nasty igt which walks
the cursor all over the place while changing the size ;-) And I guess
Ville gets to pimp his atomic update code and wm 2-stage update for this
stuff here, too.

I get a feeling this isn't quite as simple as Sagar's first patch
suggested ...
-Daniel
>  		intel_crtc_update_cursor(crtc, intel_crtc->cursor_bo != NULL);
> +	}
>  
>  	return 0;
>  fail_unpin:
> -- 
> 1.9.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch