Re: [PATCH 1/8] drm/msm/dpu: reset unassigned resource slots to NULL on topology update

[Val Packett <val@packett.cool>]

On 10/26/26 4:16 PM, Xi Zhang wrote:
> While this is not currently the case, it may be possible that topology
> for cwb and dsc resource requirements change between mode set in the
> future.
>
> e.g. when dsc support is added to DisplayPort, dsc may be optionally
> enabled and disabled between different modes due to
> bandwidth requirements.
>
> Set unassigned resource slots to NULL on topology update to avoid
> issues in the future. It's good practice to do so anyway.
>
> Signed-off-by: Xi Zhang <xz.ca.cn@gmail.com>
> ---
>   drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c | 22 +++++++++++++++-------
>   1 file changed, 15 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> index 0a6be69a3e83..8d2b4d2726f2 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> @@ -1205,9 +1205,13 @@ static void dpu_encoder_virt_atomic_mode_set(struct drm_encoder *drm_enc,
>   						       ARRAY_SIZE(hw_pp));
>   	}
>   
> -	for (i = 0; i < num_cwb; i++) {
> -		dpu_enc->hw_cwb[i] = to_dpu_hw_cwb(hw_cwb[i]);
> -		cwb_mask |= BIT(dpu_enc->hw_cwb[i]->idx - CWB_0);
> +	for (i = 0; i < ARRAY_SIZE(dpu_enc->hw_cwb); i++) {
> +		if (i < num_cwb) {
> +			dpu_enc->hw_cwb[i] = to_dpu_hw_cwb(hw_cwb[i]);
> +			cwb_mask |= BIT(dpu_enc->hw_cwb[i]->idx - CWB_0);
> +		} else {
> +			dpu_enc->hw_cwb[i] = NULL;
> +		}
>   	}
>   
>   	dpu_enc->cwb_mask = cwb_mask;
> @@ -1215,16 +1219,20 @@ static void dpu_encoder_virt_atomic_mode_set(struct drm_encoder *drm_enc,
>   	num_ctl = dpu_rm_get_assigned_resources(&dpu_kms->rm, global_state,
>   		drm_enc->crtc, DPU_HW_BLK_CTL, hw_ctl, ARRAY_SIZE(hw_ctl));
>   
> -	for (i = 0; i < MAX_CHANNELS_PER_ENC; i++)
> +	for (i = 0; i < ARRAY_SIZE(dpu_enc->hw_pp); i++)
>   		dpu_enc->hw_pp[i] = i < num_pp ? to_dpu_hw_pingpong(hw_pp[i])
>   						: NULL;
>   
>   	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 < ARRAY_SIZE(dpu_enc->hw_dsc); i++) {
> +		if (i < num_dsc) {
> +			dpu_enc->hw_dsc[i] = to_dpu_hw_dsc(hw_dsc[i]);
> +			dsc_mask |= BIT(dpu_enc->hw_dsc[i]->idx - DSC_0);
> +		} else {
> +			dpu_enc->hw_dsc[i] = NULL;
> +		}
>   	}
>   
>   	dpu_enc->dsc_mask = dsc_mask;

The radxa 7.0.11 tree which has some DP DSC patches indeed touches this 
code with "drm/msm/dpu: Clear stale DSC resources during modesets":

https://github.com/radxa/kernel/commit/d0a8968dca16965395f4089a28d48ab6acde565e

(but it only clears hw_dsc, but in the hw_pp loop, for the assigned 
resources..)

[+cc sophon]

~val