linux-kernel - Re: [RFC PATCH 0/5] USB Audio Gadget refactoring

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Date:	Wed, 27 Jul 2016 00:55:17 +0300
From:	Ruslan Bilovol <ruslan.bilovol@...il.com>
To:	Krzysztof Opasiak <k.opasiak@...sung.com>
Cc:	Jassi Brar <jassisinghbrar@...il.com>,
	Clemens Ladisch <clemens@...isch.de>,
	Felipe Balbi <balbi@...nel.org>,
	Daniel Mack <zonque@...il.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/5] USB Audio Gadget refactoring

On Tue, Jul 26, 2016 at 3:02 PM, Krzysztof Opasiak
<k.opasiak@...sung.com> wrote:
>
>
> On 07/26/2016 10:53 AM, Jassi Brar wrote:
>> On Tue, Jul 26, 2016 at 7:01 AM, Ruslan Bilovol
>> <ruslan.bilovol@...il.com> wrote:
>>> On Fri, Jul 15, 2016 at 10:43 AM, Clemens Ladisch <clemens@...isch.de> wrote:
>>>>>> On Tue, May 24, 2016 at 2:50 AM, Ruslan Bilovol
>>>>>> <ruslan.bilovol@...il.com> wrote:
>>>>>>> it may break current usecase for some people
>>>>
>>>> And what are the benefits that justify breaking the kernel API?
>>>
>>>
>>> Main limitation with current f_uac1 design is - it can be used only on systems
>>> with real ALSA card present and can have only exact number of
>>> channels / sampling rate as sink card has.
>>> Yet it is not flexible - can't do audio processing between f_uac1 and the card.
>>> Also if someone wants to bind f_uac1 it to another sound card he has to
>>> unload g_audio or reconfigure it through configfs - that means USB
>>> reenumeration on host device.
>>>
>>> If you have a "virtual sound card", audio processing is done in userspace
>>> and is more flexible. You even don't need to have a real sound card and
>>> can use some userspace application for playing/capturing audio samples.
>>> Moreover, existing f_uac2 (that is USB Audio Class 2.0 function
>>> implementation) already uses approach of "virtual sound card"
>>>
>> While I agree the virtual sound card approach is the right way, I am
>> not sure if we should break the userspace api that the existing UAC1
>> driver exposes. Maybe we should add another virtual-sound-card
>> exposing UAC1 driver ... and hopefully very similar to (or just port
>> of) the f_audio_source.c from android.
>
> Definitely agree with this opinion. I don't see any benefits of breaking
> the API here instead of adding just another USB function. Maybe even
> some pieces of code could be shared with f_uac1.c but I think that this
> should be a brand new function.
>

So if we want to keep old API working, easiest (and cleanest) way is
to create a new f_uac1.c version and kconfig symbol, for example
f_uac1_newapi.c and CONFIG_USB_F_UAC1_NEWAPI
There is no sence to share some pieces of code with f_uac1.c just
because it is changed too drastically.

So I'll implement it in v2 if there is no any objections

Best regards,
Ruslan Bilovol