[PATCH 6/8] ALSA: pcm: conditionally avoid mmap of control data

[Takashi Iwai]

On Mon, 12 Jul 2021 22:56:07 +0200,
Pierre-Louis Bossart wrote:
> 
> 
> 
> On 6/13/21 2:28 AM, Takashi Iwai wrote:
> > On Thu, 10 Jun 2021 22:53:24 +0200,
> > Pierre-Louis Bossart wrote:
> >>
> >> In case of mmap, by default alsa-lib mmaps both control and status data.
> >>
> >> If driver subscribes for application pointer update, driver needs to get
> >> notification whenever appl ptr changes. With the above case driver won't
> >> get appl ptr notifications.
> >>
> >> This patch check on a hw info flag and returns error when user land asks
> >> for mmaping control & status data, thus forcing user to issue
> >> IOCTL_SYNC_PTR.
> >>
> >> This patch was originally submitted in 2017, c.f.
> >> https://lore.kernel.org/alsa-devel/1494896518-23399-4-git-send-email-subhransu.s.prusty@intel.com/
> >>
> >> Suggested-by: Takashi Iwai <tiwai at suse.de>
> >> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
> >> Reviewed-by: Kai Vehmanen <kai.vehmanen at linux.intel.com>
> >> Reviewed-by: Ranjani Sridharan <ranjani.sridharan at linux.intel.com>
> > 
> > This kind of flag itself was what I also introduced for another
> > purpose, too.  There is a WIP patch that allows the use of
> > non-coherent non-contiguous buffer pages, and this flag would fit for
> > that.  FWIW, the patch is found at
> >   https://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git/log/?h=topic/memalloc
> 
> Sorry Takashi, I missed your feedback on this patch.
> 
> Are you saying I should use the definition in that patch?
> 
> +#define SNDRV_DMA_TYPE_NONCONTIG	8	/* non-coherent SG buffer */
> 
> I am not quite sure if how this is related to the application using mmap or not?

Not about that, but rather meant that some flag for disabling the mmap
of PCM control record would be needed for other purposes like the
above, too.  That is, this patch could be out of series and applied
beforehand in my side.


thanks,

Takashi