[alsa-devel] [PATCH 0/3] Add SPIB Support for Intel Skylake platforms

[Takashi Sakamoto]

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.

>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
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