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

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 3/17/26 4:30 PM, Dmitry Baryshkov wrote:
> Current topology code will try using 2 LMs with just one DSC, which
> breaks cases like SC7280 / Fairphone5.

(why/how?)

Konrad

>  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@fairphone.com>
> Closes: https://lore.kernel.org/r/DH1IKLU0YZYU.2SW4WYO7H3H4R@fairphone.com/
> Tested-by: Luca Weiss <luca.weiss@fairphone.com> # qcm6490-fairphone-fp5
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
> ---
>  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,