Re: [PATCH v4] drm/bridge: dw-hdmi-qp: Guard clear_audio_infoframe when PHY is down

[Cristian Ciocaltea <cristian.ciocaltea@collabora.com>]

Hi Frank,

On 5/12/26 1:31 PM, 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.
> 
> Add a tmds_char_rate guard in dw_hdmi_qp_bridge_clear_audio_infoframe().
> Decouple write_audio_infoframe from clear_audio_infoframe to avoid the
> redundant check in the write path.
> Add PKTSCHED_AMD_TX_EN to the clear mask to keep the enable/disable
> balance.
> 
> Fixes: fd0141d1a8a2 ("drm/bridge: synopsys: Add audio support for dw-hdmi-qp")
> Cc: stable@vger.kernel.org
> Signed-off-by: Frank Zhang <rmxpzlb@gmail.com>
> 
> ---
> 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@gmail.com/
> 
> 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@gmail.com/
> 
> Changes in v4:
> - Update panic stack on 7.0.5
> - Link to v3: https://lore.kernel.org/all/20260423081514.15444-1-rmxpzlb@gmail.com/
> ---
>  drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
> index d649a1cf07f5..1c18f8650fcd 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
> @@ -886,11 +886,11 @@ static int dw_hdmi_qp_bridge_clear_audio_infoframe(struct drm_bridge *bridge)
>  {
>  	struct dw_hdmi_qp *hdmi = bridge->driver_private;
>  
> -	dw_hdmi_qp_mod(hdmi, 0,
> -		       PKTSCHED_ACR_TX_EN |
> -		       PKTSCHED_AUDS_TX_EN |
> -		       PKTSCHED_AUDI_TX_EN,
> -		       PKTSCHED_PKT_EN);
> +	if (hdmi->tmds_char_rate)
> +		dw_hdmi_qp_mod(hdmi, 0,
> +			       PKTSCHED_ACR_TX_EN | PKTSCHED_AMD_TX_EN |
> +			       PKTSCHED_AUDS_TX_EN | PKTSCHED_AUDI_TX_EN,
> +			       PKTSCHED_PKT_EN);
>  
>  	return 0;
>  }
> @@ -989,7 +989,10 @@ 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_mod(hdmi, 0,
> +		       PKTSCHED_ACR_TX_EN | PKTSCHED_AMD_TX_EN |
> +		       PKTSCHED_AUDS_TX_EN | PKTSCHED_AUDI_TX_EN,
> +		       PKTSCHED_PKT_EN);

Is "avoid the redundant check in the write path" the only reason of open-coding
dw_hdmi_qp_bridge_clear_audio_infoframe()? 

Performance wise, I don't think there are any real gains here, so we'd be better
off reusing the existing code where possible.

Regards,
Cristian