Issue in pcm_dsnoop.c in alsa-lib

[S.J. Wang]

> >
> > Hi Takashi Iwai, Jaroslav Kysela
> >
> >     We encountered an issue in the pcm_dsnoop use case, could you
> > please help to have a look?
> >
> >     *Issue description:*
> >     With two instances for dsnoop type device running in parallel,
> > after suspend/resume,  one of the instances will be hung in memcpy
> > because the very large copy size is obtained.
> >
> > #3 0x0000ffffa78d5098 in snd_pcm_dsnoop_sync_ptr
> (pcm=0xaaab06563da0)
> > at pcm_dsnoop.c:158 dsnoop = 0xaaab06563c20 slave_hw_ptr = 64
> > old_slave_hw_ptr = 533120 avail = *187651522444320*
> >
> >   * Reason analysis: *
> >    The root cause that I analysis is that after suspend/resume,  one
> > instance will get the SND_PCM_STATE_SUSPENDED state from slave pcm
> device,
> >   then it will do snd_pcm_prepare() and snd_pcm_start(),  which will
> > reset the dsnoop->slave_hw_ptr and the hw_ptr of slave pcm device,
> > then the state of this instance is correct.  But another instance may
> > not get the SND_PCM_STATE_SUSPENDED state from slave pcm device
> > because slave device may have been recovered by first instance,  so
> > the dsnoop->slave_hw_ptr is not reset.  but because hw_ptr of slave
> > pcm device has been reset,  so there will be a very large "avail" size.
> >
> >    *Solution:*
> >    I didn't come up with a fix for this issue,  seems there is no easy
> > way to let another instance know this case and reset the
> > dsnoop->slave_hw_ptr,  could you please help?
> 
> Could you try topic/pcm-direct-resume branch on
> 
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> lib&data=04%7C01%7Cshengjiu.wang%40nxp.com%7C95f97de3f2c840d
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> eserved=0
> 

Thanks,  I push my test result in https://github.com/alsa-project/alsa-lib/issues/213
Could you please review?

Best regards
Wang shengjiu