[RFC 2/2] ASoC: rt5670: Add LED trigger support

[Jaroslav Kysela]

Dne 01. 03. 21 v 22:26 Hans de Goede napsal(a):
> Hi,
> 
> On 3/1/21 9:43 PM, Mark Brown wrote:
>> On Mon, Mar 01, 2021 at 08:49:34PM +0100, Hans de Goede wrote:
>>> On 3/1/21 8:15 PM, Mark Brown wrote:
>>
>>>> Off the top of my head something like writing a control name into a
>>>> sysfs file might work, it doesn't scale if you need to use multiple
>>>> controls as rt5640 does though.
>>
>>> Currently ALSA/UCM does not use sysfs files for anything, so this
>>> feels very inconsistent with how all the rest of this currently works.
>>
>> Yes, you'd really want to add string controls in ALSA.
> 
> Hmm, we already have SNDRV_CTL_ELEM_TYPE_BYTES controls. I think that will
> work nicely actually, we can have the UCM conf file send a 0 terminated
> string to the driver that way. It would be nice to have some syntactic
> sugar on the UCM side to be able to actually specify a string instead
> of an array of bytes, but I don't think we need any new userspace API
> for this.

The LEDs are controlled per machine not per card. So do we need to create the 'Speaker/Mic LED Control' control for all cards?

Also, this change sounds really generic. The interface may be implemented in my proposed control led kernel module, not in the codec drivers.

The Mark's sysfs idea is not bad in my opinion. The sequences may be extended in UCM, we have already 'exec' command. Yes, this command is a little heavy for the sysfs writes, but we can add command like 'sysset' or so for sysfs like:

  # detach all speaker LED controls for card 1
  # similar to 'echo -n "card=1,*" > /sysfs/devices/virtual/sound/ctl-led/speaker/detach'
  sysset "devices/virtual/sound/ctl-led/speaker/detach:card=1,*"

  # attach the 'Speaker Playback Switch',10 control to speaker LED trigger in card 1
  # similar to 'echo -n "card=1,iface=MIXER,name='Speaker Playback Switch',index=10" > /sysfs/devices/virtual/sound/ctl-led/speaker/attach
  sysset "devices/virtual/sound/ctl-led/speaker/attach:card=1,iface=MIXER,name='Speaker Playback Switch',index=10"

Security: The LED-control bindings should be handled only in the boot / init phase (thus in UCM BootSequence section) and the sysfs interface files should be read-only for normal users.

				Jaroslav

-- 
Jaroslav Kysela <perex at perex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.