Re: [PATCH 1/4] drm/i915: Suppress redundant syncs with mmio page flips

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Jun 18, 2014 at 12:23:14PM +0100, Chris Wilson wrote:
> Since mmio-flips do not occur on the suggested ring, we are introducing
> an extra sync operation where none is required. Pass the current
> obj->ring, which is what mmio flip will use, to pin_to_display_plane so
> that we emit the appropriate synchronisation (none).
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

I had a vague recollection that I had seen something like this and now I
found it...

The patch could use a rebase I think, and perhaps it could use a boolean
to avoid duplicating the buffer pinning in two place? I was thinking
something like:

ring = whatever;
bool mmio_flip = use_mmio_flip(ring);
if (mmio_flip)
	ring = obj->ring;
pin_and_fence(ring);
...
if (mmio_flip)
	...
else
	...

But either way this gets
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> ---
>  drivers/gpu/drm/i915/intel_display.c | 29 ++++++++++++++++++++---------
>  1 file changed, 20 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 5e8e711..55cb343 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -9492,21 +9492,32 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
>  		ring = &dev_priv->ring[RCS];
>  	}
>  
> -	ret = intel_pin_and_fence_fb_obj(dev, obj, ring);
> -	if (ret)
> -		goto cleanup_pending;
> +	if (use_mmio_flip(ring, obj)) {
> +		ret = intel_pin_and_fence_fb_obj(dev, obj, obj->ring);
> +		if (ret)
> +			goto cleanup_pending;
>  
> -	work->gtt_offset =
> -		i915_gem_obj_ggtt_offset(obj) + intel_crtc->dspaddr_offset;
> +		work->gtt_offset =
> +			i915_gem_obj_ggtt_offset(obj) + intel_crtc->dspaddr_offset;
>  
> -	if (use_mmio_flip(ring, obj))
>  		ret = intel_queue_mmio_flip(dev, crtc, fb, obj, ring,
>  					    page_flip_flags);
> -	else
> +		if (ret)
> +			goto cleanup_unpin;
> +
> +	} else {
> +		ret = intel_pin_and_fence_fb_obj(dev, obj, ring);
> +		if (ret)
> +			goto cleanup_pending;
> +
> +		work->gtt_offset =
> +			i915_gem_obj_ggtt_offset(obj) + intel_crtc->dspaddr_offset;
> +
>  		ret = dev_priv->display.queue_flip(dev, crtc, fb, obj, ring,
>  				page_flip_flags);
> -	if (ret)
> -		goto cleanup_unpin;
> +		if (ret)
> +			goto cleanup_unpin;
> +	}
>  
>  	intel_disable_fbc(dev);
>  	intel_mark_fb_busy(obj, NULL);
> -- 
> 1.9.1
> 
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-- 
Ville Syrjälä
Intel OTC