[PATCH v3 6/8] drm/msm/dpu: clear the DSC blocks left by a previous reservation

[Dmitry Baryshkov]

dpu_encoder_virt_atomic_mode_set() fills dpu_enc->hw_dsc[] with the DSC
blocks of the new reservation, but only the first num_dsc entries.  The
array is never cleared, so an encoder which once drove two DSC blocks
keeps pointing at the second one after it has been given a topology with
a single DSC.

dpu_encoder_use_dsc_merge() counts the non-NULL entries of the whole
array and compares them against the number of interfaces, so the leftover
pointer makes it report DSC merge for a topology which has none, and
dpu_encoder_prep_dsc() then programs DSC_MODE_MULTIPLEX into the only DSC
block that is really used.

Assign NULL when the new reservation has no block for the slot.

Fixes: 58dca9810749 ("drm/msm/disp/dpu1: Add support for DSC in encoder")
Assisted-by: LLM
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxxxxxxxx>
---
 drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
index 1f20695f81e3..50c49259a23e 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
@@ -1222,9 +1222,10 @@ static void dpu_encoder_virt_atomic_mode_set(struct drm_encoder *drm_enc,
 	num_dsc = dpu_rm_get_assigned_resources(&dpu_kms->rm, global_state,
 						drm_enc->crtc, DPU_HW_BLK_DSC,
 						hw_dsc, ARRAY_SIZE(hw_dsc));
-	for (i = 0; i < num_dsc; i++) {
-		dpu_enc->hw_dsc[i] = to_dpu_hw_dsc(hw_dsc[i]);
-		dsc_mask |= BIT(dpu_enc->hw_dsc[i]->idx - DSC_0);
+	for (i = 0; i < MAX_CHANNELS_PER_ENC; i++) {
+		dpu_enc->hw_dsc[i] = i < num_dsc ? to_dpu_hw_dsc(hw_dsc[i]) : NULL;
+		if (dpu_enc->hw_dsc[i])
+			dsc_mask |= BIT(dpu_enc->hw_dsc[i]->idx - DSC_0);
 	}
 
 	dpu_enc->dsc_mask = dsc_mask;

-- 
2.47.3