[alsa-devel] reset of kernel input buffer for /dev/dsp

[Amit Nagal]

Hi ,

Thanx for the patch . Application of this patch resolves kernel pcm
ring buffer flush problem .
Now SNDCTL_DSP_RESET works properly .


On a suggestive note  ,  as this bug is present in main stream kernel also ,
this patch should also be applied as well .

Thanx & Regards
Amit Nagal




On Mon, Nov 29, 2010 at 5:58 PM, Takashi Iwai <tiwai at suse.de> wrote:
> At Mon, 29 Nov 2010 17:40:03 +0900,
> Amit Nagal wrote:
>>
>> Hi ,
>>
>> Thanx for the reply .
>>
>> we tried SNDCTL_DSP_RESET , but it is not flushing  the kernel pcm
>> buffer for us  .
>
> It should.  It abandons the pending data and resets to the initial
> state before starting the stream.
>
> But, it might be a bug in OSS emulation later.  It doesn't seem to
> reset the internal buffer.  Try the patch below.
>
>> any other method which we can use ?
>
>> also please lets us the function available with alsa - lib which
>> serves the purpose of flushing
>> the kernel pcm buffer .
>
> snd_pcm_drop() corresponds to it.
>
>
> Takashi
>
> ---
> diff --git a/sound/core/oss/pcm_oss.c b/sound/core/oss/pcm_oss.c
> index 5c8c7df..a4411a3 100644
> --- a/sound/core/oss/pcm_oss.c
> +++ b/sound/core/oss/pcm_oss.c
> @@ -1510,16 +1510,19 @@ static ssize_t snd_pcm_oss_read1(struct snd_pcm_substream *substream, char __use
>  static int snd_pcm_oss_reset(struct snd_pcm_oss_file *pcm_oss_file)
>  {
>        struct snd_pcm_substream *substream;
> +       struct snd_pcm_runtime *runtime;
> +       int i;
>
> -       substream = pcm_oss_file->streams[SNDRV_PCM_STREAM_PLAYBACK];
> -       if (substream != NULL) {
> -               snd_pcm_kernel_ioctl(substream, SNDRV_PCM_IOCTL_DROP, NULL);
> -               substream->runtime->oss.prepare = 1;
> -       }
> -       substream = pcm_oss_file->streams[SNDRV_PCM_STREAM_CAPTURE];
> -       if (substream != NULL) {
> +       for (i = 0; i < 2; i++) {
> +               substream = pcm_oss_file->streams[i];
> +               if (!substream)
> +                       continue;
> +               runtime = substream->runtine;
>                snd_pcm_kernel_ioctl(substream, SNDRV_PCM_IOCTL_DROP, NULL);
> -               substream->runtime->oss.prepare = 1;
> +               runtime->oss.prepare = 1;
> +               runtime->oss.buffer_used = 0;
> +               runtime->oss.prev_hw_ptr_period = 0;
> +               runtime->oss.period_ptr = 0;
>        }
>        return 0;
>  }
>