Re: [PATCH v5] drm/bridge: dw-hdmi-qp: Guard clear_audio_infoframe when PHY is down

[Sebastian Reichel]

Hi,

On Tue, Sep 08, 2026 at 03:02:20PM +0800, Frank Zhang wrote:
> The following panic was observed during system reboot:
> 
> Kernel panic - not syncing: Asynchronous SError Interrupt
> CPU: 6 UID: 1000 PID: 2348 Comm: pipewire ... 7.0.5+ #4 PREEMPT(full)
> Call trace:
>  ...
>  regmap_update_bits_base+0x70/0xa8
>  dw_hdmi_qp_bridge_clear_audio_infoframe+0x3c/0x58 [dw_hdmi_qp]
>  drm_bridge_connector_clear_audio_infoframe+0x2c/0x48 [drm_display_helper]
>  ...
>  dw_hdmi_qp_audio_disable+0x28/0xa8 [dw_hdmi_qp]
>  drm_bridge_connector_audio_shutdown+0x38/0x68 [drm_display_helper]
>  drm_connector_hdmi_audio_shutdown+0x28/0x40 [drm_display_helper]
>  hdmi_codec_shutdown+0x60/0x90 [snd_soc_hdmi_codec]
>  ...
>  snd_pcm_release_substream+0xcc/0x120 [snd_pcm]
>  snd_pcm_release+0x4c/0xc0 [snd_pcm]
>  ...
> 
> The root cause is pipewire tries to close the HDMI audio device after
> atomic_disable(), which sets tmds_char_rate to 0 and disables the PHY.
> 
> In this case, dw_hdmi_qp_audio_disable() will call
> dw_hdmi_qp_bridge_clear_audio_infoframe(), accessing register without
> checking tmds_char_rate.
> 
> Guard the register access in drm_display_helper callback function with
> tmds_char_rate check.
> 
> Fixes: fd0141d1a8a2 ("drm/bridge: synopsys: Add audio support for dw-hdmi-qp")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Frank Zhang <rmxpzlb@xxxxxxxxx>
> 
> ---
> Changes in v2:
> - Move drm_atomic_helper_connector_hdmi_clear_audio_infoframe() inside
>   the if (hdmi->tmds_char_rate) of dw_hdmi_qp_audio_disable().
> - Link to v1: https://lore.kernel.org/all/20260416093150.13853-1-rmxpzlb@xxxxxxxxx/
> 
> Changes in v3:
> - Add a tmds_char_rate guard in clear_audio_infoframe path.
> - Decouple write_audio_infoframe from clear_audio_infoframe.
> - Balance the PKTSCHED_AMD_TX_EN bit enable/disable.
> - Link to v2: https://lore.kernel.org/all/20260418101936.7731-1-rmxpzlb@xxxxxxxxx/
> 
> Changes in v4:
> - Update panic stack on 7.0.5
> - Link to v3: https://lore.kernel.org/all/20260423081514.15444-1-rmxpzlb@xxxxxxxxx/
> 
> Changes in v5:
> - Reuse the origin dw_hdmi_qp_bridge_clear_audio_infoframe and add
>   tmds_char_rate guard in new callback function.
> - Link to v4: https://lore.kernel.org/all/20260512103153.8861-1-rmxpzlb@xxxxxxxxx/
> ---
>  drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
> index 1c214a8e6dc2..8729783d4eb6 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
> @@ -880,7 +880,7 @@ static int dw_hdmi_qp_bridge_clear_spd_infoframe(struct drm_bridge *bridge)
>  	return 0;
>  }
>  
> -static int dw_hdmi_qp_bridge_clear_audio_infoframe(struct drm_bridge *bridge)
> +static int __dw_hdmi_qp_bridge_clear_audio_infoframe(struct drm_bridge *bridge)
>  {
>  	struct dw_hdmi_qp *hdmi = bridge->driver_private;
>  
> @@ -893,6 +893,16 @@ static int dw_hdmi_qp_bridge_clear_audio_infoframe(struct drm_bridge *bridge)
>  	return 0;
>  }
>  
> +static int dw_hdmi_qp_bridge_clear_audio_infoframe(struct drm_bridge *bridge)
> +{
> +	struct dw_hdmi_qp *hdmi = bridge->driver_private;
> +
> +	if (hdmi->tmds_char_rate > 0)
> +		return __dw_hdmi_qp_bridge_clear_audio_infoframe(bridge);
> +
> +	return 0;
> +}
> +
>  static void dw_hdmi_qp_write_pkt(struct dw_hdmi_qp *hdmi, const u8 *buffer,
>  				 size_t start, size_t len, unsigned int reg)
>  {
> @@ -987,7 +997,7 @@ static int dw_hdmi_qp_bridge_write_audio_infoframe(struct drm_bridge *bridge,
>  {
>  	struct dw_hdmi_qp *hdmi = bridge->driver_private;
>  
> -	dw_hdmi_qp_bridge_clear_audio_infoframe(bridge);
> +	__dw_hdmi_qp_bridge_clear_audio_infoframe(bridge);

Why? Having the extra tmds_char_rate check being done here is not a
problem except for some extra instructions. Considering this is
definetly not a hot path, introducing the extra function is not
worth the trouble. Just patch the original function to add the check
resulting in a nice and simple 2 lines fix and you are done.

>  
>  	/*
>  	 * AUDI_CONTENTS0: { RSV, HB2, HB1, RSV }
> -- 
> 2.55.0
> 

Greetings,

-- Sebastian

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