Re: [PATCH v8 21/21] drm/bridge: synopsys: dw-dp: Add audio support

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Missing lock in dw_dp_audio_mute_stream() creates a data race on dp->audio_muted and hardware registers, leading to state inconsistency.
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--- Patch [21]: [PATCH v8 21/21] drm/bridge: synopsys: dw-dp: Add audio support ---
commit 4c38ba6f108f1bab4d60be41675a0058796ffe6a
Author: Sebastian Reichel <sebastian.reichel@collabora.com>

drm/bridge: synopsys: dw-dp: Add audio support
    
Implement audio support for the Synopsys DesignWare DisplayPort controller.

> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-dp.c b/drivers/gpu/drm/bridge/synopsys/dw-dp.c
> index a39007f13a052..a62fca20ac2fe 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-dp.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-dp.c

[ ... ]

> +static int __dw_dp_audio_enable(struct dw_dp *dp)
> +{

[ ... ]

> +	regmap_update_bits(dp->regmap, DW_DP_AUD_CONFIG1,
> +			   AUDIO_DATA_IN_EN | NUM_CHANNELS | AUDIO_DATA_WIDTH |
> +			   AUDIO_INF_SELECT | HBR_MODE_ENABLE | AUDIO_MUTE,
> +			   FIELD_PREP(AUDIO_DATA_IN_EN, audio_data_in_en) |
> +			   FIELD_PREP(NUM_CHANNELS, dp->audio_channels - 1) |
> +			   FIELD_PREP(AUDIO_DATA_WIDTH, dp->audio_sample_width) |
> +			   FIELD_PREP(AUDIO_INF_SELECT, dp->audio_interface) |
> +			   FIELD_PREP(HBR_MODE_ENABLE, 0) |
> +			   FIELD_PREP(AUDIO_MUTE, dp->audio_muted));

[ ... ]

> +static int dw_dp_audio_mute_stream(struct drm_bridge *bridge,
> +				   struct drm_connector *connector,
> +				   bool enable, int direction)
> +{
> +	struct dw_dp *dp = bridge_to_dp(bridge);
> +
> +	dev_dbg(dp->dev, "audio %smute\n", enable ? "" : "un");
> +
> +	dp->audio_muted = enable;
> +
> +	regmap_update_bits(dp->regmap, DW_DP_AUD_CONFIG1, AUDIO_MUTE,
> +			   FIELD_PREP(AUDIO_MUTE, enable));
> +
> +	return 0;
> +}

[Severity: Medium]
Does this function need to hold dp->audio_lock when modifying dp->audio_muted
and the DW_DP_AUD_CONFIG1 register?

If ALSA calls dw_dp_audio_mute_stream() concurrently with a modeset that is
calling __dw_dp_audio_enable(), could it lead to a desync between the hardware
state and dp->audio_muted?

For example, if __dw_dp_audio_enable() reads dp->audio_muted as false, and
before it writes to DW_DP_AUD_CONFIG1, dw_dp_audio_mute_stream() executes,
updates dp->audio_muted to true, and successfully mutes the hardware.

Would __dw_dp_audio_enable() then overwrite the hardware register with its
stale false value, leaving the audio stream unexpectedly unmuted?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260731-synopsys-dw-dp-improvements-v8-0-ac1e6a75782f@collabora.com?part=21