Re: [PATCH 0/3] Add SPIB Support for Intel Skylake platforms

["Subhransu S. Prusty" <subhransu.s.prusty@intel.com>]

On Tue, Jan 30, 2018 at 04:08:39PM +0530, Takashi Sakamoto wrote:
> Hi,
> 
> On Jan 30 2018 18:36, Sriram Periyasamy wrote:
> > Skylake audio controller supports SPIB (Software Position in buffer)
> > capability, which can be used to inform position of application pointer
> > to host DMA controller. When SPIB mode is enabled, driver could write
> > the application pointer position in SPIB register. Host DMA will make
> > sure it won't read/write beyond bytes specified in SPIB register.
> > 
> > SPIB mode will be useful in low power use cases, where DSP could
> > pre-fetch large buffers to avoid frequent wakes caused due to interrupts.
> > 
> > To support SPIB in the driver, save the spib values in stream context
> > which can be restored during resume from S3. Add new hw_params flag to
> > explicitly tell driver that rewinds will never be used.
> > 
> > Pierre-Louis Bossart (1):
> >   ALSA: core: let low-level driver or userspace disable rewinds
> > 
> > Ramesh Babu (2):
> >   ALSA: hda: ext: add spib to stream context
> >   ASoC: Intel: Skylake: Add support for spib mode
> > 
> >  include/sound/hdaudio_ext.h       |  1 +
> >  include/sound/pcm.h               |  1 +
> >  include/uapi/sound/asound.h       |  1 +
> >  sound/core/pcm_native.c           |  8 ++++++++
> >  sound/hda/ext/hdac_ext_stream.c   |  2 ++
> >  sound/soc/intel/skylake/skl-pcm.c | 43 ++++++++++++++++++++++++++++++++++++++-
> >  6 files changed, 55 insertions(+), 1 deletion(-)
> 
> In my opinion, when drivers
> return appropriate values at implementations of
> "struct snd_pcm_ops.pointer" and "struct snd_pcm_ops.ack", your aim is
> satisfied. In short, you can let ALSA PCM core to handle
> rewinding/forwarding requests from userland for zero number of handled
> frames in result. So the 'SNDRV_PCM_HW_PARAMS_NO_REWINDS' flag is
> useless.

Based on the earlier discussion in v3, this series includes the usage of the
'SNDRV_PCM_HW_PARAMS_NO_REWINDS' flag. Please refer to the discussion on
https://patchwork.kernel.org/patch/9795233/

> 
> From me, please refer to our previous discussion about this
> flag[1][2][3], then describe your insistence of this flag. At least,
> it's not better idea to abandon the old discussion when posting this
> kind of patches. Additionally you should add 'v4' in title of this

Yes should have added the reference and v4. Sorry to have missed it.

Regards,
Subhransu

> patchset to represent this patchset is a part of series of your work for
> the flag and your Intel platform.
> 
> [1]
> http://mailman.alsa-project.org/pipermail/alsa-devel/2017-May/120676.html
> [2]
> http://mailman.alsa-project.org/pipermail/alsa-devel/2017-June/121683.html
> [3]
> http://mailman.alsa-project.org/pipermail/alsa-devel/2017-June/121967.html
> 
> 
> Regards
> 
> Takashi Sakamoto
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