Re: [PATCH] usb-audio: Fix boot-time crackling for Generic USB Audio device

[Zhang Heng]

> Please add some comment why the device needs this workaround.
> IIUC, the reason is different from the others in your case.
>
> Also, please verify that the problem is reproduced in the latest
> upstream kernel, and the workaround works as expected there, too.
>
>
> thanks,
>
> Takashi

>> --- a/sound/usb/quirks.c
>> +++ b/sound/usb/quirks.c
>> @@ -1938,6 +1938,10 @@ void snd_usb_endpoint_start_quirk(struct 
snd_usb_endpoint *ep)
>>   	    ep->type == SND_USB_ENDPOINT_TYPE_SYNC)
>>   		ep->skip_packets = 4;
>>
>> +	if (ep->chip->usb_id == USB_ID(0x1e0b, 0xd01e) &&
>> +	    ep->type == SND_USB_ENDPOINT_TYPE_SYNC)
>> +		ep->skip_packets = 4;
>> +

Let me update the current status: that piece of code can be
omitted. I have applied your test patch, but there is no
change. It might be that your patch has no effect on this
device. I tested with version v7.2-rc1. To be honest,
without any modification, the problem becomes a reproducible
stutter plus crackling noise. After applying my fix, it
becomes a probabilistic stutter (still with a relatively
high probability of recurrence), but when there is no
stutter, there is also no crackling noise. So I am sure
that this patch is at least useful, but it does not
perfectly solve the problem. I am still trying to resolve
the stutter issue, and I wonder if it is due to resource
contention during boot? This problem only occurs at boot
time; after entering the system, it disappears.