Re: [PATCH v8 19/21] drm/bridge: synopsys: dw-dp: Use regmap_set_bits in dw_dp_send_sdp

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] A mutex is acquired in dw_dp_send_sdp(), which is called from the bridge's atomic enable path, violating atomic context rules.
--

--- Patch [19]: [PATCH v8 19/21] drm/bridge: synopsys: dw-dp: Use regmap_set_bits in dw_dp_send_sdp ---
commit fbf6588f46fe1b8bc7ef347644cccb5c7a752410
Author: Sebastian Reichel <[email protected]>

drm/bridge: synopsys: dw-dp: Use regmap_set_bits in dw_dp_send_sdp

This commit simplifies dw_dp_send_sdp() by making use of regmap_set_bits
instead of regmap_update_bits. No functional change is intended.

> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-dp.c b/drivers/gpu/drm/bridge/synopsys/dw-dp.c
> --- a/drivers/gpu/drm/bridge/synopsys/dw-dp.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-dp.c
> @@ -1070,14 +1070,12 @@ static int dw_dp_send_sdp(struct dw_dp *dp, struct dw_dp_sdp *sdp)

[Severity: High]
Does this function sleep in an atomic context?

Looking at dw_dp_send_sdp(), it acquires a sleeping lock via
scoped_guard(mutex, &dp->sdp_lock) earlier in the function. However, this
is called from the bridge's atomic enable path:

drm_atomic_helper_commit_tail()
  -> dw_dp_bridge_atomic_enable()
    -> dw_dp_video_enable()
      -> dw_dp_send_vsc_sdp()
        -> dw_dp_send_sdp()

Can this sequence cause a kernel splat ("BUG: sleeping function called from
invalid context") or potential deadlocks when modesetting, since it executes
within drm_atomic_helper_commit_tail() where sleeping is forbidden?

>  			     FIELD_PREP(SDP_REGS, get_unaligned_le32(payload)));
>  
>  	if (sdp->flags & DW_DP_SDP_VERTICAL_INTERVAL)
> -		regmap_update_bits(dp->regmap, DW_DP_SDP_VERTICAL_CTRL,
> -				   EN_VERTICAL_SDP << nr,
> -				   EN_VERTICAL_SDP << nr);
> +		regmap_set_bits(dp->regmap, DW_DP_SDP_VERTICAL_CTRL,
> +				EN_VERTICAL_SDP << nr);
>  
>  	if (sdp->flags & DW_DP_SDP_HORIZONTAL_INTERVAL)
> -		regmap_update_bits(dp->regmap, DW_DP_SDP_HORIZONTAL_CTRL,
> -				   EN_HORIZONTAL_SDP << nr,
> -				   EN_HORIZONTAL_SDP << nr);
> +		regmap_set_bits(dp->regmap, DW_DP_SDP_HORIZONTAL_CTRL,
> +				EN_HORIZONTAL_SDP << nr);
>  
>  	return nr;
>  }

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260731-synopsys-dw-dp-improvements-v8-0-ac1e6a75782f@collabora.com?part=19