On some systems there can be a race condition in which no crtc state is
added to the first atomic commit. This results in all crtc's having a
null DDB allocation, causing a FIFO underrun on any update until the
first modeset.
Reported-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Inspired-by: Mahesh Kumar <mahesh1.kumar@xxxxxxxxx>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Fixes: 98d39494d375 ("drm/i915/gen9: Compute DDB allocation at atomic
check time (v4)")
Cc: <stable@xxxxxxxxxxxxxxx> # v4.8+
Cc: Mahesh Kumar <mahesh1.kumar@xxxxxxxxx>
Cc: Matt Roper <matthew.d.roper@xxxxxxxxx>
---
drivers/gpu/drm/i915/intel_pm.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index a488e068c3d6..8daa382b47f3 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -5037,10 +5037,27 @@ skl_compute_wm(struct drm_atomic_state *state)
struct drm_crtc_state *cstate;
struct intel_atomic_state *intel_state = to_intel_atomic_state(state);
struct skl_wm_values *results = &intel_state->wm_results;
+ struct drm_device *dev = state->dev;
struct skl_pipe_wm *pipe_wm;
bool changed = false;
int ret, i;
+ if (to_i915(dev)->wm.distrust_bios_wm) {
+ changed = true;
+
+ /*
+ * The first commit after driver load must update the ddb
+ * allocations, so make sure we at least hold a lock to
+ * inspect the state required for watermark updates.
+ *
+ * Below we'll grab the required crtc state.
+ */
+ ret = drm_modeset_lock(&dev->mode_config.connection_mutex,
+ state->acquire_ctx);
+ if (ret)
+ return ret;
+ }
+
/*
* If this transaction isn't actually touching any CRTC's, don't
* bother with watermark calculation. Note that if we pass this
@@ -5051,6 +5068,7 @@ skl_compute_wm(struct drm_atomic_state *state)
*/
for_each_new_crtc_in_state(state, crtc, cstate, i)
changed = true;
+
if (!changed)
return 0;
--
2.11.0
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