Re: [PATCH 02/26] drm/i915: don't stop+start FBC at every flip

Chris Wilson
2015-10-27T19:50:49Z

On Tue, Oct 27, 2015 at 02:50:04PM -0200, Paulo Zanoni wrote:
> @@ -1021,13 +1078,48 @@ void intel_fbc_flush(struct drm_i915_private *dev_priv,
> if (origin == ORIGIN_GTT)
> return;
>
> + /* Hardware tracking already recompresses the CFB (nuke) for us if FBC
> + * is enabled and we do a page flip, so we can safely ignore it here.
> + * FBC may be disabled in case we got an invalidate() before the
> + * flush(), so we'll still have to check that case below. */

I feel like I understand what is going on a bit better now, thanks!

> + if (origin == ORIGIN_FLIP && dev_priv->fbc.enabled)
> + return;
> +
> mutex_lock(&dev_priv->fbc.lock);
>
> dev_priv->fbc.busy_bits &= ~frontbuffer_bits;
>
> if (!dev_priv->fbc.busy_bits) {
> - __intel_fbc_disable(dev_priv);
> - __intel_fbc_update(dev_priv);
> + if (origin == ORIGIN_FLIP) {

Note this test here is redundant.

We know that for an origin == FLIP to be here, FBC is disabled and
calling intel_fbc_disable() is then a no-op.

So it turns out that the origin two lines of disable(); update() works
just as well. Or is there some later patch that tweaks this branch
further?
-Chris

--
Chris Wilson, Intel Open Source Technology Centre