drm/i915/fbc: Reduce fbc1 compression interval to 1 second

The default fbc1 compression interval we use is 500 frames. That
translates to over 8 seconds typically. That's rather excessive
so let's drop it to 1 second.

The hardware will not attempt recompression unless at least one
line has been modified, so a shorter compression interval should
not cause extra bandwidth use in the purely idle scenario. Of
course in the mostly idle case we are possibly going to recompress
a bit more.

Should really try to find some kind of sweet spot to minimize
the energy usage...
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200429101034.8208-11-ville.syrjala@linux.intel.comReviewed-by: José Roberto de Souza <jose.souza@intel.com>

drivers/gpu/drm/i915/display/intel_fbc.c

@@ -698,8 +698,8 @@ static void intel_fbc_update_state_cache(struct intel_crtc *crtc,
 	cache->fb.stride = fb->pitches[0];
 	cache->fb.modifier = fb->modifier;
 
-	/* This value was pulled out of someone's hat */
-	cache->interval = 500;
+	/* FBC1 compression interval: arbitrary choice of 1 second */
+	cache->interval = drm_mode_vrefresh(&crtc_state->hw.adjusted_mode);
 
 	cache->fence_y_offset = intel_plane_fence_y_offset(plane_state);