[alsa-devel] [PATCH 2/7] ALSA: core: add .update_appl_ptr callback for pcm ops

[Takashi Iwai]

On Fri, 30 Sep 2016 14:43:25 +0200,
Subhransu S. Prusty wrote:
> 
> From: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
> 
> When appl_ptr is updated let low-level driver know, e.g.  to let the
> low-level driver/hardware pre-fetch data opportunistically.
> 
> The existing .ack callback could be used but it would need to be
> extended with new arguments, resulting in multiple changes in legacy
> code.

I wouldn't mind changing these callers.  They aren't so many, after
all. 


Takashi

> Instead a new .appl_ptr_update callback is added.  The difference
> between .ack and .appl_ptr_update is that .ack is only called on read or
> write. .appl_ptr_update is called on read, write, rewind, forward or
> when updating the appl_ptr from userspace.
> 
> In the ALSA core, this capability is independent from the NO_REWIND
> hardware flag. The low-level driver may however tie both options and
> only use the updated appl_ptr when rewinds are disabled due to hardware
> limitations.
> 
> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
> Signed-off-by: Babu, Ramesh <ramesh.babu at intel.com>
> Signed-off-by: Vinod Koul <vinod.koul at intel.com>
> Signed-off-by: Subhransu S. Prusty <subhransu.s.prusty at intel.com>
> ---
>  include/sound/pcm.h     |  1 +
>  sound/core/pcm_lib.c    |  6 ++++++
>  sound/core/pcm_native.c | 24 +++++++++++++++++++++++-
>  3 files changed, 30 insertions(+), 1 deletion(-)
> 
> diff --git a/include/sound/pcm.h b/include/sound/pcm.h
> index 5344c16..1accb8b 100644
> --- a/include/sound/pcm.h
> +++ b/include/sound/pcm.h
> @@ -87,6 +87,7 @@ struct snd_pcm_ops {
>  			     unsigned long offset);
>  	int (*mmap)(struct snd_pcm_substream *substream, struct vm_area_struct *vma);
>  	int (*ack)(struct snd_pcm_substream *substream);
> +	int (*appl_ptr_update)(struct snd_pcm_substream *substream);
>  };
>  
>  /*
> diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
> index bb12615..1656ca9 100644
> --- a/sound/core/pcm_lib.c
> +++ b/sound/core/pcm_lib.c
> @@ -2090,6 +2090,9 @@ static snd_pcm_sframes_t snd_pcm_lib_write1(struct snd_pcm_substream *substream,
>  		if (substream->ops->ack)
>  			substream->ops->ack(substream);
>  
> +		if (substream->ops->appl_ptr_update)
> +			substream->ops->appl_ptr_update(substream);
> +
>  		offset += frames;
>  		size -= frames;
>  		xfer += frames;
> @@ -2322,6 +2325,9 @@ static snd_pcm_sframes_t snd_pcm_lib_read1(struct snd_pcm_substream *substream,
>  		if (substream->ops->ack)
>  			substream->ops->ack(substream);
>  
> +		if (substream->ops->appl_ptr_update)
> +			substream->ops->appl_ptr_update(substream);
> +
>  		offset += frames;
>  		size -= frames;
>  		xfer += frames;
> diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
> index be8617b..c56d4ed 100644
> --- a/sound/core/pcm_native.c
> +++ b/sound/core/pcm_native.c
> @@ -2475,6 +2475,10 @@ static snd_pcm_sframes_t snd_pcm_playback_rewind(struct snd_pcm_substream *subst
>  		appl_ptr += runtime->boundary;
>  	runtime->control->appl_ptr = appl_ptr;
>  	ret = frames;
> +
> +	if (substream->ops->appl_ptr_update)
> +		substream->ops->appl_ptr_update(substream);
> +
>   __end:
>  	snd_pcm_stream_unlock_irq(substream);
>  	return ret;
> @@ -2526,6 +2530,10 @@ static snd_pcm_sframes_t snd_pcm_capture_rewind(struct snd_pcm_substream *substr
>  		appl_ptr += runtime->boundary;
>  	runtime->control->appl_ptr = appl_ptr;
>  	ret = frames;
> +
> +	if (substream->ops->appl_ptr_update)
> +		substream->ops->appl_ptr_update(substream);
> +
>   __end:
>  	snd_pcm_stream_unlock_irq(substream);
>  	return ret;
> @@ -2575,6 +2583,10 @@ static snd_pcm_sframes_t snd_pcm_playback_forward(struct snd_pcm_substream *subs
>  		appl_ptr -= runtime->boundary;
>  	runtime->control->appl_ptr = appl_ptr;
>  	ret = frames;
> +
> +	if (substream->ops->appl_ptr_update)
> +		substream->ops->appl_ptr_update(substream);
> +
>   __end:
>  	snd_pcm_stream_unlock_irq(substream);
>  	return ret;
> @@ -2624,6 +2636,10 @@ static snd_pcm_sframes_t snd_pcm_capture_forward(struct snd_pcm_substream *subst
>  		appl_ptr -= runtime->boundary;
>  	runtime->control->appl_ptr = appl_ptr;
>  	ret = frames;
> +
> +	if (substream->ops->appl_ptr_update)
> +		substream->ops->appl_ptr_update(substream);
> +
>   __end:
>  	snd_pcm_stream_unlock_irq(substream);
>  	return ret;
> @@ -2723,8 +2739,14 @@ static int snd_pcm_sync_ptr(struct snd_pcm_substream *substream,
>  			return err;
>  	}
>  	snd_pcm_stream_lock_irq(substream);
> -	if (!(sync_ptr.flags & SNDRV_PCM_SYNC_PTR_APPL))
> +	if (!(sync_ptr.flags & SNDRV_PCM_SYNC_PTR_APPL)) {
> +		/* boundary wrap-around is assumed to be handled in userspace */
>  		control->appl_ptr = sync_ptr.c.control.appl_ptr;
> +
> +		/* let low-level driver know about appl_ptr change */
> +		if (substream->ops->appl_ptr_update)
> +			substream->ops->appl_ptr_update(substream);
> +	}
>  	else
>  		sync_ptr.c.control.appl_ptr = control->appl_ptr;
>  	if (!(sync_ptr.flags & SNDRV_PCM_SYNC_PTR_AVAIL_MIN))
> -- 
> 1.9.1
>