[PATCH v3 3/6] drm/i915/skl: Only flush pipes when we change the ddb allocation

[Lyude <cpaul@redhat.com>]

Manual pipe flushes are only necessary in order to make sure that we prevent
pipes with changed ddb allocations from overlapping from one another at
any point in time. Additionally, forcing us to wait for the next vblank
every time we have to update the watermark values because the cursor was
moving between screens will introduce a rather noticable lag for users.

Signed-off-by: Lyude <cpaul@redhat.com>
Cc: stable@vger.kernel.org
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
---
 drivers/gpu/drm/i915/i915_drv.h |  1 +
 drivers/gpu/drm/i915/intel_pm.c | 31 +++++++++++++++++++++++++++++--
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 1f6fe8c..d65e897 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1597,6 +1597,7 @@ struct skl_ddb_allocation {
 
 struct skl_wm_values {
 	unsigned dirty_pipes;
+	bool ddb_changed;
 	struct skl_ddb_allocation ddb;
 	uint32_t wm_linetime[I915_MAX_PIPES];
 	uint32_t plane[I915_MAX_PIPES][I915_MAX_PLANES][8];
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 9546f13..b6618fd 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -3897,6 +3897,12 @@ static void skl_flush_wm_values(struct drm_i915_private *dev_priv,
 	new_ddb = &new_values->ddb;
 	cur_ddb = &dev_priv->wm.skl_hw.ddb;
 
+	/* We only ever need to flush when the ddb allocations change */
+	if (!new_values->ddb_changed)
+		return;
+
+	new_values->ddb_changed = false;
+
 	/*
 	 * First pass: flush the pipes with the new allocation contained into
 	 * the old space.
@@ -4001,6 +4007,22 @@ pipes_modified(struct drm_atomic_state *state)
 	return ret;
 }
 
+static bool
+skl_pipe_ddb_changed(struct skl_ddb_allocation *old,
+		     struct skl_ddb_allocation *new,
+		     enum pipe pipe)
+{
+	if (memcmp(&old->pipe[pipe], &new->pipe[pipe],
+		   sizeof(old->pipe[pipe])) != 0 ||
+	    memcmp(&old->plane[pipe], &new->plane[pipe],
+		   sizeof(old->plane[pipe])) != 0 ||
+	    memcmp(&old->y_plane[pipe], &new->y_plane[pipe],
+		   sizeof(old->y_plane[pipe])) != 0)
+		return true;
+
+	return false;
+}
+
 static int
 skl_compute_ddb(struct drm_atomic_state *state)
 {
@@ -4008,7 +4030,8 @@ skl_compute_ddb(struct drm_atomic_state *state)
 	struct drm_i915_private *dev_priv = to_i915(dev);
 	struct intel_atomic_state *intel_state = to_intel_atomic_state(state);
 	struct intel_crtc *intel_crtc;
-	struct skl_ddb_allocation *ddb = &intel_state->wm_results.ddb;
+	struct skl_ddb_allocation *new_ddb = &intel_state->wm_results.ddb;
+	struct skl_ddb_allocation *old_ddb = &dev_priv->wm.skl_hw.ddb;
 	uint32_t realloc_pipes = pipes_modified(state);
 	int ret;
 
@@ -4046,9 +4069,13 @@ skl_compute_ddb(struct drm_atomic_state *state)
 		if (IS_ERR(cstate))
 			return PTR_ERR(cstate);
 
-		ret = skl_allocate_pipe_ddb(cstate, ddb);
+		ret = skl_allocate_pipe_ddb(cstate, new_ddb);
 		if (ret)
 			return ret;
+
+		if (!intel_state->wm_results.ddb_changed &&
+		    skl_pipe_ddb_changed(old_ddb, new_ddb, intel_crtc->pipe))
+			intel_state->wm_results.ddb_changed = true;
 	}
 
 	return 0;
-- 
2.7.4