On Tue, 20 Mar 2018 17:01:06 +0100,
Sriram Periyasamy wrote:
>
> From: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>
>
> Add new hw_params flag to explicitly tell driver that rewinds will never
> be used. This can be used by low-level driver to optimize DMA operations
> and reduce power consumption. Use this flag only when data written in
> ring buffer will never be invalidated, e.g. any update of appl_ptr is
> final.
>
> Note that the update of appl_ptr include both a read/write data
> operation as well as snd_pcm_forward() whose behavior is not modified.
>
> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>
> Signed-off-by: Ramesh Babu <ramesh.babu@xxxxxxxxx>
> Signed-off-by: Subhransu S. Prusty <subhransu.s.prusty@xxxxxxxxx>
> Signed-off-by: Sriram Periyasamy <sriramx.periyasamy@xxxxxxxxx>
Well, I'm still not convinced with this flag.
First off, does it really need to be per PCM stream? The introducing
something to hw_parms implies that it varies per application. But I
can't imagine that a system requires different behavior per stream
regarding such a thing.
Second, the driver can implement a check in PCM ack callback to
prevent the rewind, too. Then there is no need to touch the PCM
core.
thanks,
Takashi
> ---
> include/sound/pcm.h | 1 +
> include/uapi/sound/asound.h | 1 +
> sound/core/pcm_native.c | 8 ++++++++
> 3 files changed, 10 insertions(+)
>
> diff --git a/include/sound/pcm.h b/include/sound/pcm.h
> index e054c583d3b3..f60397eb4aab 100644
> --- a/include/sound/pcm.h
> +++ b/include/sound/pcm.h
> @@ -379,6 +379,7 @@ struct snd_pcm_runtime {
> unsigned int rate_num;
> unsigned int rate_den;
> unsigned int no_period_wakeup: 1;
> + unsigned int no_rewinds:1;
>
> /* -- SW params -- */
> int tstamp_mode; /* mmap timestamp is updated */
> diff --git a/include/uapi/sound/asound.h b/include/uapi/sound/asound.h
> index ed0a120d4f08..ff57e4c89de4 100644
> --- a/include/uapi/sound/asound.h
> +++ b/include/uapi/sound/asound.h
> @@ -377,6 +377,7 @@ typedef int snd_pcm_hw_param_t;
> #define SNDRV_PCM_HW_PARAMS_NORESAMPLE (1<<0) /* avoid rate resampling */
> #define SNDRV_PCM_HW_PARAMS_EXPORT_BUFFER (1<<1) /* export buffer */
> #define SNDRV_PCM_HW_PARAMS_NO_PERIOD_WAKEUP (1<<2) /* disable period wakeups */
> +#define SNDRV_PCM_HW_PARAMS_NO_REWINDS (1<<3) /* disable rewinds */
>
> struct snd_interval {
> unsigned int min, max;
> diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
> index 77ba50ddcf9e..4616420cdbf7 100644
> --- a/sound/core/pcm_native.c
> +++ b/sound/core/pcm_native.c
> @@ -692,6 +692,8 @@ static int snd_pcm_hw_params(struct snd_pcm_substream *substream,
> runtime->no_period_wakeup =
> (params->info & SNDRV_PCM_INFO_NO_PERIOD_WAKEUP) &&
> (params->flags & SNDRV_PCM_HW_PARAMS_NO_PERIOD_WAKEUP);
> + runtime->no_rewinds =
> + (params->flags & SNDRV_PCM_HW_PARAMS_NO_REWINDS) ? 1 : 0;
>
> bits = snd_pcm_format_physical_width(runtime->format);
> runtime->sample_bits = bits;
> @@ -2614,6 +2616,9 @@ static snd_pcm_sframes_t snd_pcm_playback_rewind(struct snd_pcm_substream *subst
> if (frames == 0)
> return 0;
>
> + if (runtime->no_rewinds)
> + return -ENODEV;
> +
> snd_pcm_stream_lock_irq(substream);
> ret = do_pcm_hwsync(substream);
> if (!ret)
> @@ -2632,6 +2637,9 @@ static snd_pcm_sframes_t snd_pcm_capture_rewind(struct snd_pcm_substream *substr
> if (frames == 0)
> return 0;
>
> + if (runtime->no_rewinds)
> + return -ENODEV;
> +
> snd_pcm_stream_lock_irq(substream);
> ret = do_pcm_hwsync(substream);
> if (!ret)
> --
> 2.7.4
>
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