[alsa-devel] Have multiple opens removed on one device?

[Scott Jiang]

2011/8/22 Mark Brown <broonie at opensource.wolfsonmicro.com>:
> On Mon, Aug 22, 2011 at 12:15:58PM +0200, Takashi Iwai wrote:
>> Scott Jiang wrote:
>
>> > In kernel 2.6.34 I can use aplay to play audio at the same time, alsa
>> > will mix the audio.
>
>> No, kernel part doesn't do such a thing.  If it's mixed, it must be
>> in the user-space (either dmix or a daemon like pulseaudio), unless
>> you hardware can do mixing by itself.
>
> There *are* some cards (mostly older ones like emu10k) that support
> multiple streams transparently but this has never been supported in
> ASoC due a lack of hardware that can do it.
>

Hi Mark,

Indeed we use dmix. But now we can't open the same device twice.
Our alsa lib and utils version is 1.0.18.
The test command: aplay 1.wav &; aplay 1.wav
In 2.6.34, strace
open("/dev/snd/pcmC0D0p", O_RDWR|O_NONBLOCK) = 4
open("/dev/snd/pcmC0D0p", O_RDWR|O_APPEND|O_NONBLOCK) = 4

In 3.0, strace
open("/dev/snd/pcmC0D0p", O_RDWR|O_NONBLOCK) = 4
open("/dev/snd/pcmC0D0p", O_RDWR|O_NONBLOCK) = -1 EBUSY (Device or
resource busy)

The O_APPEND flag missed in new kernel. But we use the same lib and
utils. It's strange.
And I found the prefer subdevice changes from 0 to -1. These two
changes cause kernel return device busy.

Mark, can you do this simple test on your board? I appreciate your
help. Thank you very much.

Regards,
Scott