[alsa-devel] [PATCH] ALSA: usb-audio: Recurse before saving terminal properties

[Daniel Mack]

Hi,

On 08/14/2015 03:25 PM, Julian Scheel wrote:
> Am 14.08.2015 um 15:06 schrieb Takashi Iwai:

>>> @@ -715,15 +715,16 @@ static int check_input_term(struct mixer_build *state, int id,
>>>   				term->name = d->iTerminal;
>>>   			} else { /* UAC_VERSION_2 */
>>>   				struct uac2_input_terminal_descriptor *d = p1;
>>> -				term->type = le16_to_cpu(d->wTerminalType);
>>> -				term->channels = d->bNrChannels;
>>> -				term->chconfig = le32_to_cpu(d->bmChannelConfig);
>>> -				term->name = d->iTerminal;
>>>
>>>   				/* call recursively to get the clock selectors */
>>>   				err = check_input_term(state, d->bCSourceID, term);
>>>   				if (err < 0)
>>>   					return err;
>>> +
>>> +				term->type = le16_to_cpu(d->wTerminalType);
>>> +				term->channels = d->bNrChannels;
>>> +				term->chconfig = le32_to_cpu(d->bmChannelConfig);
>>> +				term->name = d->iTerminal;
>>
>> ... by this override, essentially all fields except for id are
>> restored.  Then what's the point to call check_input_term() for the
>> clock source?
> 
> This is a good point indeed, but due do my understanding the recursion 
> is not about filling missing information, but about verifying a valid 
> descriptor. So in case there are broken references in the descriptor it 
> gets abandoned. I'm happy to be corrected if this understanding is wrong.

Hmm, good point. It' been a while since I worked on this, but looking at
the code right now, you're right, the mixer unit for input terminal is
indeed just overridden by the information of the clock selector on UAC2.
That doesn't seem right.

I guess what we really want is to add a 2nd mixer control in such cases,
and that would mean we need to call into parse_audio_selector_unit()
instead.

I can cook up or test a patch next week, when I have access to test
hardware.


Thanks,
Daniel