[PATCH] drm/msm/dpu: don't try using 2 LMs if only one DSC is available

[Dmitry Baryshkov]

Current topology code will try using 2 LMs with just one DSC, which
breaks cases like SC7280 / Fairphone5. Forbid using 2 LMs split in such
a case.

Fixes: 1ce69c265a53 ("drm/msm/dpu: move resource allocation to CRTC")
Reported-by: Luca Weiss <luca.weiss@xxxxxxxxxxxxx>
Closes: https://lore.kernel.org/r/DH1IKLU0YZYU.2SW4WYO7H3H4R@xxxxxxxxxxxxx/
Tested-by: Luca Weiss <luca.weiss@xxxxxxxxxxxxx> # qcm6490-fairphone-fp5
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxxxxxxxx>
---
 drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
index 6bf7c46379ae..96b67ea3fb4c 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
@@ -1410,7 +1410,8 @@ static struct msm_display_topology dpu_crtc_get_topology(
 		topology.num_lm = 2;
 	else if (topology.num_dsc == 2)
 		topology.num_lm = 2;
-	else if (dpu_kms->catalog->caps->has_3d_merge)
+	else if (dpu_kms->catalog->caps->has_3d_merge &&
+		 topology.num_dsc == 0)
 		topology.num_lm = (mode->hdisplay > MAX_HDISPLAY_SPLIT) ? 2 : 1;
 	else
 		topology.num_lm = 1;

---
base-commit: 50c4a49f7292b33b454ea1a16c4f77d6965405dc
change-id: 20260317-fix-3d-dsc-4b073977ea19

Best regards,
-- 
With best wishes
Dmitry