Re: [PATCH 3/3] usb: gadget: u_audio: add real feedback implementation

[Pavel Hofman <pavel.hofman@ivitera.com>]

Dne 09. 11. 20 v 9:24 Pavel Hofman napsal(a):
> Hi Ruslan,
> 
> Dne 08. 11. 20 v 1:18 Ruslan Bilovol napsal(a):
>> This adds interface between userspace and feedback
>> endpoint to report real feedback frequency to the Host.
>>
>> Current implementation adds new userspace interface
>> ALSA mixer control "PCM Feedback Frequency Hz" (similar
>> to aloop driver's "PCM Rate Shift 100000" mixer control)
>>
>> We allow +/-20% deviation of nominal sampling frequency,
>> that usually is more than enough in real-world usecases
>>
>> Usage of this new control is easy to implement in
>> existing userspace tools like alsaloop from alsa-utils.
>>
>> Signed-off-by: Ruslan Bilovol <ruslan.bilovol@gmail.com>
>> ---
>>   drivers/usb/gadget/function/f_uac2.c  |  4 ++
>>   drivers/usb/gadget/function/u_audio.c | 93 +++++++++++++++++++++++++++++++++++
>>   drivers/usb/gadget/function/u_audio.h |  7 +++
>>   3 files changed, 104 insertions(+)
> 
> Thanks a lot for the great implementation. IIUC the control element sets
> integer frequency in Hz. Often the clocks deviate by small fractions of
> Hz. Please have you considered the value to be e.g. in 100th of Hz for
> finer control of the samplerate? Similar to the PCM Rate Shift which has
> a step 100000th of the samplerate.
> 

My stupid, I did not realize that one Hz in the samplerate value is 
basically the same order of magnitude as the 100,000ths in the "PCM Rate 
Shift 100000" mixer control. Sorry for disturbing.

Thanks,

Pavel.