On Fri, 30 Sep 2016 14:43:24 +0200, Subhransu S. Prusty 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. > > Caveat: there is currently no way to query capabilities without opening > a pcm stream, so applications might need to serially open all exposed > devices, check what they support by looking at hw_params->info and close > them (this is what PulseAudio does so might not be an issue) This is a general issue in the current PCM API design, and not specific to this new bit. > Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx> > Signed-off-by: Ramesh Babu <ramesh.babu@xxxxxxxxx> > Signed-off-by: Vinod Koul <vinod.koul@xxxxxxxxx> > Signed-off-by: Subhransu S. Prusty <subhransu.s.prusty@xxxxxxxxx> > --- > 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 af1fb37..5344c16 100644 > --- a/include/sound/pcm.h > +++ b/include/sound/pcm.h > @@ -368,6 +368,7 @@ 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 609cadb..6828ed2 100644 > --- a/include/uapi/sound/asound.h > +++ b/include/uapi/sound/asound.h > @@ -362,6 +362,7 @@ 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 c61fd50..be8617b 100644 > --- a/sound/core/pcm_native.c > +++ b/sound/core/pcm_native.c > @@ -565,6 +565,8 @@ 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; > @@ -2438,6 +2440,9 @@ static snd_pcm_sframes_t snd_pcm_playback_rewind(struct snd_pcm_substream *subst > if (frames == 0) > return 0; > > + if (runtime->no_rewinds) > + return 0; Better to return an error instead? > snd_pcm_stream_lock_irq(substream); > switch (runtime->status->state) { > case SNDRV_PCM_STATE_PREPARED: > @@ -2486,6 +2491,9 @@ static snd_pcm_sframes_t snd_pcm_capture_rewind(struct snd_pcm_substream *substr > if (frames == 0) > return 0; > > + if (runtime->no_rewinds) > + return 0; Ditto. Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel