Dne 13. 01. 22 v 16:08 Jaroslav Kysela napsal(a):
On 13. 01. 22 14:45, Takashi Iwai wrote:
Also ideally, there may be a check in hw_params, if parameters
(buffers) are changed, but the implementation is not so easy. Maybe we
can allow OPEN ->
PREPARE transition for this case, so the applications may just restart
the streaming in the most light way.
Hmm. Reading more about those restrictions and requirements, I feel
that this might be better implemented in the gadget driver side
locally at first. Basically we can handle similarly: add a new local
flag, set it at the stream stop, and return an error at prepare until
hw_params gets reconfigured. This might be even smaller changes?
Pavel reported that stop to SETUP is not enough for sox, but it's true
that the driver may fail in the prepare() callback until the standard
stream operation is not recovered. I think that sox is trying to recover
and it succeeds - then the I/O timeout occurs.
Ref:
https://lore.kernel.org/alsa-devel/9635d70f-dc12-f9ed-29f5-ce34a1d4b112@xxxxxxxxxxx/
The gadget driver (drivers/usb/gadget/function/u_audio.c) has empty
prepare callback at the moment.
Pavel, could you try to add the no-stream flag management to the gadget
driver and return an error in the prepare callback in this case?
My apology for the delay. I can make the changes to the gadget to be
prepared for the alsa change. Let me recap to see if I understand your
plan correctly:
* Currently the stopped stream is indicated by unsetting prm->active
https://kernel.googlesource.com/pub/scm/linux/kernel/git/gregkh/usb/+/554237f2bb62c4fcf01372e4c63d3e0062f27bac/drivers/usb/gadget/function/u_audio.c#502
.
* A hw_params_set flag indicating that hw params have been configured
should be set at
https://kernel.googlesource.com/pub/scm/linux/kernel/git/gregkh/usb/+/554237f2bb62c4fcf01372e4c63d3e0062f27bac/drivers/usb/gadget/function/u_audio.c#423
. Where should it be unset? At snd_pcm_ops.stop (currently empty), at
https://kernel.googlesource.com/pub/scm/linux/kernel/git/gregkh/usb/+/554237f2bb62c4fcf01372e4c63d3e0062f27bac/drivers/usb/gadget/function/u_audio.c#494
for active = false, or somewhere else?
* A check should be added to snd_pcm_ops.prepare which fails if the
hw_params_set flag is unset. What error type should the fail return?
Thanks a lot for help.
Best regards,
Pavel.
