On Fri, Sep 30, 2016 at 03:40:45PM +0200, Takashi Iwai wrote: > On Fri, 30 Sep 2016 14:43:26 +0200, > Subhransu S. Prusty wrote: > > > > From: Ramesh Babu <ramesh.babu@xxxxxxxxx> > > > > In case of mmap, by default alsa-lib mmaps both control & status data. > > > > If driver subscribes for .appl_ptr_update, driver needs to get > > notification whenever appl ptr changes. So with control & status mmaped, > > driver won't get appl ptr notifications. > > > > In alsa-lib IOCTL_SYNC_PTR can be forced using sync_ptr_ioctl flag in > > conf But this makes driver behavior dependent on a flag in the conf. > > > > This patch conditionally checks for .appl_ptr_update and returns error > > when user land asks for mmaping control & status data, thus forcing user > > to issue IOCTL_SYNC_PTR. > > > > One drawback with this approach is, if .appl_ptr_update is subscribed by > > driver, the user space looses flexibility to mmap the control & status > > data. > > Yes, and it can be seen as an obvious regression, so I'm not sure > whether this condition is the best choice. > > OTOH, I now understand why you need it in this way -- alsa-lib does > mmap ctrl/status pages at snd_pcm_open() and sync_ptr is used only as > a fallback. So, one solution would be to fix alsa-lib side. Or, if > we fix the kernel in this way, it would work with old alsa-lib, but it > has another penalty. Hmm... I will check if it can be fixed in alsa-lib side. Regards, Subhransu > > -- _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
