[alsa-devel] [PATCH 2/2] sound: usb: allow clock source validity interrupts

[Daniel Mack]

On 04/09/2016 10:52 AM, Takashi Iwai wrote:
> On Fri, 08 Apr 2016 19:52:02 +0200,
> Daniel Mack wrote:
>>
>> miniDSP USBStreamer UAC2 devices send clock validity changes with the
>> control field set to zero. The current interrupt handler ignores all
>> packets if the control field does not match the mixer element's, but
>> it really should only do that in case that field is needed to
>> distinguish multiple elements with the same ID.
>>
>> This patch implements a logic that lets notifications packets pass
>> if the element ID is unique for a given device.
>>
>> Signed-off-by: Daniel Mack <daniel at zonque.org>
>> ---
>>  sound/usb/mixer.c | 9 ++++++++-
>>  1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
>> index 973274b..aa6f16e 100644
>> --- a/sound/usb/mixer.c
>> +++ b/sound/usb/mixer.c
>> @@ -2371,6 +2371,7 @@ static void snd_usb_mixer_interrupt_v2(struct usb_mixer_interface *mixer,
>>  	__u8 unitid = (index >> 8) & 0xff;
>>  	__u8 control = (value >> 8) & 0xff;
>>  	__u8 channel = value & 0xff;
>> +	unsigned int count = 0;
>>  
>>  	if (channel >= MAX_CHANNELS) {
>>  		usb_audio_dbg(mixer->chip,
>> @@ -2379,6 +2380,12 @@ static void snd_usb_mixer_interrupt_v2(struct usb_mixer_interface *mixer,
>>  		return;
>>  	}
>>  
>> +	for (list = mixer->id_elems[unitid]; list; list = list->next_id_elem)
>> +		count++;
>> +
>> +	if (count == 0)
>> +		return;
>> +
>>  	for (list = mixer->id_elems[unitid]; list; list = list->next_id_elem) {
>>  		struct usb_mixer_elem_info *info;
>>  
>> @@ -2386,7 +2393,7 @@ static void snd_usb_mixer_interrupt_v2(struct usb_mixer_interface *mixer,
>>  			continue;
>>  
>>  		info = (struct usb_mixer_elem_info *)list;
>> -		if (info->control != control)
>> +		if (count > 1 && info->control != control)
>>  			continue;
> 
> Just for checking count=0 and count=1, we need no loop to count
> beforehand.
> 		if (info->control != control &&
> 		    (list != mixer->id_elems[unit] ||
> 		     list->list_next_id_elem))
> 			continue;
> 
> But, this doesn't look better and is more harder to understand, so I'm
> not willing to sell it :)

I had something like that before but opted for the more readable
version. But you're right. I'll add a comment and do it your way.


Thanks!
Daniel