[alsa-devel] [PATCH 1/2] ALSA: pcm - Ensure wakeup at each periodic interrupt

[Takashi Iwai]

At Thu, 17 Dec 2009 15:00:02 +0900,
jassisinghbrar at gmail.com wrote:
> 
> From: Jassi Brar <jassi.brar at samsung.com>
> 
> The check for at least 'avail_min' available data before calling wake_up
> doesn't always hold good as it does not guarantee callbacks at each periodic
> interrupt.

Well, avail_min can be greater than period_size.  And, avail_min won't be
less than period size.

For example, when avail_min = 2.5 x period_size, the driver wakes up
in periods like 3, 2, 3, 2, ...

> An example of such situation is snd_pcm_lib_read1/write1 consuming some space
> of the period and going to sleep from wait_for_avail_min upon syncing with
> the DMA pointer. Clearly just the remainder of period size is needed, but
> wake_up is called only after _two_ periodic interrupts from that point.

In that case, the original behavior is correct.


thanks,

Takashi

> 
> Signed-off-by: Jassi Brar <jassi.brar at samsung.com>
> ---
>  sound/core/pcm_lib.c |   10 ++++++++--
>  1 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
> index 30f4108..ee2d7b9 100644
> --- a/sound/core/pcm_lib.c
> +++ b/sound/core/pcm_lib.c
> @@ -189,7 +189,7 @@ snd_pcm_update_hw_ptr_pos(struct snd_pcm_substream *substream,
>  static int snd_pcm_update_hw_ptr_post(struct snd_pcm_substream *substream,
>  				      struct snd_pcm_runtime *runtime)
>  {
> -	snd_pcm_uframes_t avail;
> +	snd_pcm_uframes_t avail, prd_short;
>  
>  	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
>  		avail = snd_pcm_playback_avail(runtime);
> @@ -208,8 +208,14 @@ static int snd_pcm_update_hw_ptr_post(struct snd_pcm_substream *substream,
>  			return -EPIPE;
>  		}
>  	}
> -	if (avail >= runtime->control->avail_min)
> +
> +	prd_short = runtime->period_size
> +			- runtime->status->hw_ptr % runtime->period_size;
> +
> +	if (avail >= runtime->control->avail_min
> +			|| avail >= prd_short)
>  		wake_up(&runtime->sleep);
> +
>  	return 0;
>  }
>  
> -- 
> 1.6.2.5
>