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[PATCH v5 0/4] USB Audio Gadget refactoring

Hi Felipe,

This is v5 of audio gadget refactoring.
Note, that legacy f_uac1 function is broken since v4.10
by commit 7e4da3fcf7c9 ("usb: gadget: composite: Test
get_alt() presence instead of set_alt()"). The fact that
at v4.12-rc5 time nobody cares about may be a good sign
that number of users is small if any. Thus making it
legacy makes sence.

This series depends on legacy f_uac1 fix I posted before:
Without this fix it's not possible to check that refactoring
didn't break legacy f_uac1 functionality


I came to this patch series when wanted to do two things:
 - use UAC1 as virtual ALSA sound card on gadget side,
   just like UAC2 is used so it's possible to do rate
 - have both playback/capture support in UAC1

Since I wanted to have same behavior for both UAC1/UAC2,
obviously I've got an utility part (u_audio.c) for
virtual ALSA sound card handling like we have
for ethernet(u_ether) or serial(u_serial) functions.
Function-specific parts (f_uac1/f_uac2) became almost 
as storage for class-specific USB descriptors, some
boilerplate for configfs, binding and few USB
config request handling.

Originally in RFC [1] I've posted before, there was
major change to f_uac1 after that it couldn't do
direct play to existing ALSA sound card anymore,
representing audio on gadget side as virtual
ALSA sound card where audio streams are simply
sinked to and sourced from it, so it may break
current usecase for some people (and that's why
it was RFC).

During RFC discussion, it was agreed to not touch
existing f_uac1 implementation and create new one
instead. At v4 patchet discussion another approach
was agreed - current f_uac1.c gets renamed to
f_uac1_legacy.c and introduced a *new* f_uac1.c
instead that is done in current patchset (v5)

Now, it's possible to use existing user-space
applications for audio routing between Audio Gadget
and real sound card. I personally use alsaloop tool
from alsautils and have ability to create PCM
loopback between two different ALSA cards using
rate resampling, which was not possible with previous
"direct play to ALSA card" approach in f_uac1. 

While here, also dropped redundant platform
driver/device creation in f_uac2 driver (as well as
didn't add "never implemented" volume/mute functionality
in f_uac1_legacy to f_uac1) that made this work even
easier to do.

This series is tested with both legacy g_audio.ko and
modern configfs approaches under Ubuntu 14.04 (UAC1 and
UAC2) and under Windows7 x64 (UAC1 only) having
perfect results in all cases.

Comments, testing are welcome.

v5 changes:
 - after discussion with Felipe, switched to another
   approach with making current f_uac1 legacy and
   introducing a new f_uac1.c instead
 - addressed Jassi's copyright comments

v4 changes:
 - renamed f_uac1_newapi to f_uac1_acard that is
   more meaningful
 - rebased on top of balbi/next

v3 changes:
 - renamed u_audio exported symbols so they don't
   conflict with old f_uac1 if both are built-in.

v2 changes:
 - do not touch f_uac1, instead created f_uac1_newapi
 - added documentation for f_uac1_newapi
 - rebased on top of v4.8-rc1

[1] https://lkml.org/lkml/2016/5/23/649

Ruslan Bilovol (4):
  usb: gadget: f_uac2: remove platform driver/device creation
  usb: gadget: f_uac2: split out audio core
  usb: gadget: function: make current f_uac1 implementation legacy
  usb: gadget: add f_uac1 variant based on a new u_audio api

 Documentation/ABI/testing/configfs-usb-gadget-uac1 |   18 +-
 .../ABI/testing/configfs-usb-gadget-uac1_legacy    |   12 +
 Documentation/usb/gadget-testing.txt               |   53 +-
 drivers/usb/gadget/Kconfig                         |   29 +-
 drivers/usb/gadget/function/Makefile               |    5 +-
 drivers/usb/gadget/function/f_uac1.c               |  906 +++++++----------
 drivers/usb/gadget/function/f_uac1_legacy.c        | 1021 ++++++++++++++++++++
 drivers/usb/gadget/function/f_uac2.c               |  795 ++-------------
 drivers/usb/gadget/function/u_audio.c              |  662 +++++++++++++
 drivers/usb/gadget/function/u_audio.h              |   95 ++
 drivers/usb/gadget/function/u_uac1.h               |   87 +-
 .../gadget/function/{u_uac1.c => u_uac1_legacy.c}  |    7 +-
 drivers/usb/gadget/function/u_uac1_legacy.h        |   82 ++
 drivers/usb/gadget/legacy/Kconfig                  |   15 +-
 drivers/usb/gadget/legacy/audio.c                  |   55 +-
 15 files changed, 2494 insertions(+), 1348 deletions(-)
 create mode 100644 Documentation/ABI/testing/configfs-usb-gadget-uac1_legacy
 create mode 100644 drivers/usb/gadget/function/f_uac1_legacy.c
 create mode 100644 drivers/usb/gadget/function/u_audio.c
 create mode 100644 drivers/usb/gadget/function/u_audio.h
 rename drivers/usb/gadget/function/{u_uac1.c => u_uac1_legacy.c} (98%)
 create mode 100644 drivers/usb/gadget/function/u_uac1_legacy.h