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@xxxxxxxxx/ > > Suggested-by: Takashi Iwai <tiwai@xxxxxxx> > Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx> > Reviewed-by: Kai Vehmanen <kai.vehmanen@xxxxxxxxxxxxxxx> > Reviewed-by: Ranjani Sridharan <ranjani.sridharan@xxxxxxxxxxxxxxx> 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 Takashi
