Re: [PATCH 2/3] ALSA: core: modify .ack callback to take arguments for updating appl ptr

[Vinod Koul <vinod.koul@intel.com>]

On Fri, May 19, 2017 at 08:27:40AM +0200, Takashi Iwai wrote:
> On Fri, 19 May 2017 05:57:05 +0200,
> Takashi Sakamoto wrote:
> > 
> > Hi,
> > 
> > On May 16 2017 10:01, Subhransu S. Prusty wrote:
> > > From: Pierre-Louis Bossart <pierre-louis.bossart@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 is extended with new attribute argument, to
> > > support this capability. Legacy driver subscribe to SND_PCM_ACK_LEGACY and
> > > doesn't process ack if it is not set. SND_PCM_ACK_APP_PTR can be used to
> > > process the application ptr update in the driver like in the skylake
> > > driver which can use this to inform position of appl pointer to host DMA
> > > controller. The skylake driver to process the SND_PCM_ACK_APP_PTR will be
> > > submitted with a separate patch set.
> > >
> > > 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@linux.intel.com>
> > > Signed-off-by: Jaikrishna Nemallapudi <jaikrishnax.nemallapudi@intel.com>
> > > Signed-off-by: Subhransu S. Prusty <subhransu.s.prusty@intel.com>
> > > ---
> > >   include/sound/pcm-indirect.h  |  4 ++--
> > >   include/sound/pcm.h           |  8 +++++++-
> > >   sound/core/pcm_lib.c          |  6 ++++--
> > >   sound/core/pcm_native.c       | 24 +++++++++++++++++++++++-
> > >   sound/mips/hal2.c             | 14 +++++++++++---
> > >   sound/pci/cs46xx/cs46xx_lib.c | 18 ++++++++++++++----
> > >   sound/pci/emu10k1/emupcm.c    |  8 ++++++--
> > >   sound/pci/rme32.c             | 15 ++++++++++++---
> > >   8 files changed, 79 insertions(+), 18 deletions(-)
> > 
> > I think it better to take care of
> > 'drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c' as
> > well. This is a driver for sound functionality of Raspberry PI 1/zero
> > and some people may still get influences from this work.
> > 
> > $ git grep -A20 'struct snd_pcm_ops' v4.12-rc1 | grep \\.ack
> > v4.12-rc1:drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c-...
> > ...
> 
> Yep, we need to cover all codes if we really change the PCM ops.

Yes and fortunately there are a large set, so conversion is not a big issue
here, converging to best approach is :)

-- 
~Vinod