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 10:01:04AM -0500, Pierre-Louis Bossart wrote:
> On 5/19/17 1:27 AM, 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.
> 
> The reason precisely why I preferred to avoid mucking with the
> existing .ack(). we have a risk of introducing problems for legacy
> and staging, not to mention out-of-tree.

Patching them should be fine, and I wont mind breaking out-of tree ones,
isn't that a good thing :)

-- 
~Vinod