[PATCH v1] Fix the possible wm overwriting

[Stanislav Lisovskiy]

Currently whenever we attempt to recalculate
watermarks, we assign dirty_pipes to zero,
then compare current wm results to the recalculated
one and if they changed we set correspondent dirty_pipes
bit again.
This can lead to if we have wm results overwriting and
clearing dirty_pipes, so that kernel we still think that
watermarks don't need to be updated, which then might
lead to fifo underruns, crc mismatch and other pleasures.

Instead, whenever we detect that wm results are changed,
need to set correspondent dirty_pipes bit and clear it
only once the change is written.

Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>
---
 drivers/gpu/drm/i915/intel_pm.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index dc034617febb..f7fbc4bc0d43 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -5441,9 +5441,6 @@ skl_compute_wm(struct drm_atomic_state *state)
 	bool changed = false;
 	int ret, i;
 
-	/* Clear all dirty flags */
-	results->dirty_pipes = 0;
-
 	ret = skl_ddb_add_affected_pipes(state, &changed);
 	if (ret || !changed)
 		return ret;
@@ -5496,6 +5493,7 @@ static void skl_atomic_update_crtc_wm(struct intel_atomic_state *state,
 	struct drm_i915_private *dev_priv = to_i915(state->base.dev);
 	struct skl_pipe_wm *pipe_wm = &cstate->wm.skl.optimal;
 	const struct skl_ddb_allocation *ddb = &state->wm_results.ddb;
+	struct skl_ddb_values *results = &state->wm_results;
 	enum pipe pipe = crtc->pipe;
 	enum plane_id plane_id;
 
@@ -5512,6 +5510,10 @@ static void skl_atomic_update_crtc_wm(struct intel_atomic_state *state,
 			skl_write_cursor_wm(crtc, &pipe_wm->planes[plane_id],
 					    ddb);
 	}
+
+	/* Clear correspondent dirty bit */
+	results->dirty_pipes &= ~drm_crtc_mask(&crtc->base);
+
 }
 
 static void skl_initial_wm(struct intel_atomic_state *state,
-- 
2.17.1