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

[Frank Zhang <rmxpzlb@gmail.com>]

On 9/8/26 20:10, Sebastian Reichel wrote:
> 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@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/
>>
>> 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@gmail.com/
>> ---
>>   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.
Add tmds_char_rate check in the original function 
`dw_hdmi_qp_bridge_clear_audio_infoframe` discussed in v1, Detlev 
Casanova recommend no need to check for tmds_char_rate in every
dw_hdmi_qp_bridge_clear_audio_infoframe() call.>
>>   
>>   	/*
>>   	 * AUDI_CONTENTS0: { RSV, HB2, HB1, RSV }
>> -- 
>> 2.55.0
>>
> 
> Greetings,
> 
> -- Sebastian