[PATCH v10 6/9] drm/i915/fbc: avoid calling fbc activate if fbc is active

[Vinod Govindapillai <vinod.govindapillai@intel.com>]

If FBC is already active, we don't need to call FBC activate
routine again unless there are changes to the fences. So skip
this on all platforms that don't have fences. Any FBC register
updates done after enabling the dirty rect support in xe3 will
trigger nuke by FBC which is counter productive to the fbc
dirty rect feature.

The front buffer rendering sequence will call intel_fbc_flush()
and which will call intel_fbc_nuke() or intel_fbc_activate()
based on FBC status explicitly and won't get impacted by this
change.

v2: use HAS_FBC_DIRTY_RECT()
    move this functionality within intel_fbc_activate()

v3: update to intel_fbc_activate logic (Ville)
    update to the patch description

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Vinod Govindapillai <vinod.govindapillai@intel.com>
---
 drivers/gpu/drm/i915/display/intel_fbc.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_fbc.c b/drivers/gpu/drm/i915/display/intel_fbc.c
index 33142427f121..ca44cec73fd2 100644
--- a/drivers/gpu/drm/i915/display/intel_fbc.c
+++ b/drivers/gpu/drm/i915/display/intel_fbc.c
@@ -734,8 +734,19 @@ static void intel_fbc_nuke(struct intel_fbc *fbc)
 
 static void intel_fbc_activate(struct intel_fbc *fbc)
 {
+	struct intel_display *display = fbc->display;
+
 	lockdep_assert_held(&fbc->lock);
 
+	/* only the fence can change for a flip nuke */
+	if (fbc->active && !intel_fbc_has_fences(display))
+		return;
+	/*
+	 * In case of FBC dirt rect, any updates to the FBC registers will
+	 * trigger the nuke.
+	 */
+	drm_WARN_ON(display->drm, fbc->active && HAS_FBC_DIRTY_RECT(display));
+
 	intel_fbc_hw_activate(fbc);
 	intel_fbc_nuke(fbc);
 
-- 
2.43.0