Re: [PATCH v2] drm/bridge: dw-hdmi-qp: Guard clear_audio_infoframe when PHY is down

[Frank Zhang <rmxpzlb@gmail.com>]

On 4/20/26 17:00, Dmitry Baryshkov wrote:
> On Mon, Apr 20, 2026 at 02:11:28PM +0800, Frank Zhang wrote:
>> On 4/19/26 08:40, Dmitry Baryshkov wrote:
>>> On Sat, Apr 18, 2026 at 06:19:36PM +0800, Frank Zhang wrote:
>>>> The following panic was observed during system reboot:
>>>>
>>>> Kernel panic - not syncing: Asynchronous SError Interrupt
>>>> CPU: 7 UID: 1000 PID: 2637 Comm: pipewire ... 6.19.10-300.fc44.aarch64
>>>> Call trace:
>>>>    ...
>>>>    regmap_update_bits_base+0x5c/0x90
>>>>    dw_hdmi_qp_bridge_clear_infoframe+0xb0/0x120 [dw_hdmi_qp]
>>>>    drm_bridge_connector_clear_infoframe+0x28/0x48 [drm_display_helper]
>>>>    ...
>>>>    dw_hdmi_qp_audio_disable+0x24/0xb8 [dw_hdmi_qp]
>>>>    drm_bridge_connector_audio_shutdown+0x30/0x60 [drm_display_helper]
>>>>    drm_connector_hdmi_audio_shutdown+0x24/0x38 [drm_display_helper]
>>>>    hdmi_codec_shutdown+0x60/0x90 [snd_soc_hdmi_codec]
>>>>    ...
>>>>    snd_pcm_release_substream.part.0+0x44/0xd8 [snd_pcm]
>>>>    snd_pcm_release+0x60/0xe8 [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 disable the PHY.
>>>>
>>>> In this case, dw_hdmi_qp_audio_disable() will call
>>>> drm_atomic_helper_connector_hdmi_clear_audio_infoframe() directly,
>>>> accessing registers without checking tmds_char_rate.
>>>>
>>>> Move drm_atomic_helper_connector_hdmi_clear_audio_infoframe() inside the
>>>> if (hdmi->tmds_char_rate) of dw_hdmi_qp_audio_disable().
>>>>
>>>> Fixes: fd0141d1a8a2 ("drm/bridge: synopsys: Add audio support for dw-hdmi-qp")
>>>> 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/
>>>>
>>>> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
>>>> index d649a1cf07f5..7760527484c8 100644
>>>> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
>>>> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
>>>> @@ -526,10 +526,10 @@ static void dw_hdmi_qp_audio_disable(struct drm_bridge *bridge,
>>>>    {
>>>>    	struct dw_hdmi_qp *hdmi = dw_hdmi_qp_from_bridge(bridge);
>>>> -	drm_atomic_helper_connector_hdmi_clear_audio_infoframe(connector);
>>>> -
>>>> -	if (hdmi->tmds_char_rate)
>>>> +	if (hdmi->tmds_char_rate) {
>>>> +		drm_atomic_helper_connector_hdmi_clear_audio_infoframe(connector);
>>>>    		dw_hdmi_qp_audio_disable_regs(hdmi);
>>>> +	}
>>>
>>> Will audio and audio infoframe remain disabled after consequetive
>>> atomic_enable() call?
>>>
>>>>    }
>>>>    static int dw_hdmi_qp_i2c_read(struct dw_hdmi_qp *hdmi,
>>>> -- 
>>>> 2.53.0
>>>>
>>>
>>
>> Sorry, I missed clearing the audio infoframe when the PHY is down. The next
>> atomic_enable() will write the stale audio infoframe. My mistake.
>>
>> To clear the stale audio infoframe, dw_hdmi_qp_audio_disable() can handle it
>> in the else branch directly, but this seems like a layering violation for a
>> bridge driver
>>
>> I think the better approach is to add a 'reset_audio_infoframe' interface in
>> drm_hdmi_state_helper.c that does basically the same as
>> drm_atomic_helper_connector_hdmi_clear_audio_infoframe(), but only clearing
>> the software state without calling clear_infoframe(). It's also a bit odd
>> since it would only be used by dw-hdmi-qp.
> 
> That sounds too fine-grained and it also will not work straight ahead...
> 
> Just for my understanding, let's consider the opposite situation: the
> user tries to start audio playback before setting the mode. How is it
> handled in the driver?
> 

audio_prepare() will return -ENODEV before the mode is set.

I admit modifying dw-hdmi-qp is more reasonable. I have a new approach:

dw-hdmi-qp should have an internal function to clear the audio infoframe 
related registers.
dw_hdmi_qp_bridge_clear_audio_infoframe() should check tmds_char_rate, 
call the new function only when tmds_char_rate is available.
dw_hdmi_qp_bridge_write_audio_infoframe() should call the new function 
directly instead of dw_hdmi_qp_bridge_clear_audio_infoframe(), without 
checking tmds_char_rate.
dw_hdmi_qp_audio_disable() doesn't need any modification.

With this approach, clear_audio_infoframe guards register access by 
checking tmds_char_rate, while write_audio_infoframe does not need to 
check it again. How about it?

Thanks,
Frank Zhang

>>
>> I'd like to get the maintainers' opinion about adding such an interface.
>>
>> Thanks,
>> Frank Zhang
>>
>