[alsa-devel] [PATCH 0/5] ALSA: firewire-tascam: support notification of

[Takashi Sakamoto]

Hi,

Units of TASCAM FireWire series transfer its state in tx isochronous
packets. The way to handle change of the state is a longstanding issue
since I firstly reveal the mechanism in this list[1].

In this time, Scott Bahling dedicates for further investigation to seek
better implementation[2][3][4]. Finally, we identified meaning of the
most of bits in the image of state, and decided which changes are worth
for userspace applications to handle as events.

This commit adds support notification of the events. Userspace
applications can handle the notification via ALSA hwdep interface.
Furthermore, they can retrieve image of the latest states via the
interface.

Changes from the initial proposal[5]:
 - obsolete usage of mmap(2) due to several disadvantages. Instead, use
   event queue for change notification, and add ioctl command to retrieve
   image of states.

Changes from the latest work[6]:
 - To reduce time in an interrupt context in which tx isochronous packets
   are handled, data in the event and the image is passed to userspace in
   big-endian order. Additionally, image of the states are passed to
   userspace in big-endian order as well. Userspace applications are
   responsible to convert the data in host-endianness order.
 - improve efficiency to copy batch of events to userspace in hwdep
   interface
 - rename structure and macro name.

This patchset is also available in my remote branch for backport purpose
to Linux v4.17 or later[7].

I've already prepare userspace implementation; libhinwa. A
'topic/firewire-tascam-pr' remote branch includes patchset for the
additional feature[8]. This library produces GObject class to handle the
event notification and emits GObject signal, and has a method
'HinawaSndTscm.get_state()', with enough consideration to endianness.
Developers can process change of state with these two APIs.

> Scott

As the above, I changed method name from 'HinawaSndTscm.get_status()'.
I'd like you to change your local implementation for 'hinawa-utils'.
Sorry to add further work to you.

[1] http://mailman.alsa-project.org/pipermail/alsa-devel/2015-July/094817.html
[2] http://mailman.alsa-project.org/pipermail/alsa-devel/2018-September/140051.html
[3] http://mailman.alsa-project.org/pipermail/alsa-devel/2018-October/140593.html
[4] http://mailman.alsa-project.org/pipermail/alsa-devel/2018-November/141395.html
[5] https://github.com/takaswie/snd-firewire-improve/tree/topic/tascam-userspace
[6] https://github.com/takaswie/snd-firewire-improve/tree/topic/tascam-userspace-take3
[7] https://github.com/takaswie/snd-firewire-improve/tree/topic/tascam-userspace-pr
[8] https://github.com/takaswie/libhinawa/tree/topic/tascam-userspace-pr

Regards

Takashi Sakamoto (5):
  ALSA: firewire-tascam: pick up data of state from tx isochronous
    pakcets
  ALSA: firewire-tascam: add new hwdep ioctl command to get state image
  ALSA: firewire-tascam: queue events for change of control surface
  ALSA: firewire-tascam: apply small refactoring to handle several type
    of event for hwdep interface
  ALSA: firewire-tascam: notify events of change of state for userspace
    applications

 include/uapi/sound/firewire.h        |  20 +++++
 sound/firewire/tascam/amdtp-tascam.c |  51 +++++++++++-
 sound/firewire/tascam/tascam-hwdep.c | 115 +++++++++++++++++++++++----
 sound/firewire/tascam/tascam.h       |   9 +++
 4 files changed, 180 insertions(+), 15 deletions(-)

-- 
2.19.1