Can I stop sound from driver as system error ?

Can I stop sound from driver as system error ?

[Kuninori Morimoto]

Hi

I wonder can I stop sound from driver side (not from user-land)
as system error during playback or capture ?
How to do it if we can ?

Best regards
---
Kuninori Morimoto

Re: Can I stop sound from driver as system error ?

[Takashi Sakamoto]

Hi,

On Dec 15 2015 10:25, Kuninori Morimoto wrote:
> I wonder can I stop sound from driver side (not from user-land)
> as system error during playback or capture ?
> How to do it if we can ?

Stop PCM substreams with SNDRV_PCM_STATE_XRUN. In detail, see 
implementation of snd_pcm_stop_xrun() available in 3.19 or later. Then, 
userspace applications cannot continue to read/write PCM frames via ALSA 
uapi.

When using alsa-lib, then, userspace applications receive -EPIPE as 
return value of calling PCM APIs. The applications can stop their 
operation for PCM character devices, or can also recover the XRUN state 
of PCM substream by calling snd_pcm_prepare(). In this case, struct 
snd_pcm_ops.prepare() is called again in driver side.

I think tinyalsa works almost the same.


Regards

Takashi Sakamoto

Re: Can I stop sound from driver as system error ?

[Kuninori Morimoto]

Hi Takashi

> > I wonder can I stop sound from driver side (not from user-land)
> > as system error during playback or capture ?
> > How to do it if we can ?
> 
> Stop PCM substreams with SNDRV_PCM_STATE_XRUN. In detail, see
> implementation of snd_pcm_stop_xrun() available in 3.19 or
> later. Then, userspace applications cannot continue to read/write PCM
> frames via ALSA uapi.
> 
> When using alsa-lib, then, userspace applications receive -EPIPE as
> return value of calling PCM APIs. The applications can stop their
> operation for PCM character devices, or can also recover the XRUN
> state of PCM substream by calling snd_pcm_prepare(). In this case,
> struct snd_pcm_ops.prepare() is called again in driver side.
> 
> I think tinyalsa works almost the same.

Thank you for detail explanation !
I will try/investigate it

Best regards
---
Kuninori Morimoto

Re: Can I stop sound from driver as system error ?

[Takashi Sakamoto]

Hi,

On Dec 15 2015 11:47, Kuninori Morimoto wrote:
>>> I wonder can I stop sound from driver side (not from user-land)
>>> as system error during playback or capture ?
>>> How to do it if we can ?
>>
>> Stop PCM substreams with SNDRV_PCM_STATE_XRUN. In detail, see
>> implementation of snd_pcm_stop_xrun() available in 3.19 or
>> later. Then, userspace applications cannot continue to read/write PCM
>> frames via ALSA uapi.
>>
>> When using alsa-lib, then, userspace applications receive -EPIPE as
>> return value of calling PCM APIs. The applications can stop their
>> operation for PCM character devices, or can also recover the XRUN
>> state of PCM substream by calling snd_pcm_prepare(). In this case,
>> struct snd_pcm_ops.prepare() is called again in driver side.
>>
>> I think tinyalsa works almost the same.
>
> Thank you for detail explanation !
> I will try/investigate it

The state of PCM substreams can be changed by process context, software 
IRQ (softIRQ) context and hardware IRQ (hardIRQ) context. Therefore, 
ALSA PCM core uses spin_lock_irqsave()/spin_lock_irqrestore() to manage 
the race condition with softIRQ disabled, hardIRQ disabled and 
kernel-preemption disabled in local processor core.

As a glance, snd-soc-rcar in upstream pushes many operations to PCM 
trigger processing, while this trigger processing is protected with the 
critical section.

When you program the xrun handling in hardware/software IRQ context, 
it's better to pay enough attention to the lock, because any process 
contexts can spin in some processor cores.


Regards

Takashi Sakamoto