Messages in this thread | | | Subject | Re: [PATCH v3 5/6] ALSA: xen-front: Implement ALSA virtual sound driver | From | Oleksandr Andrushchenko <> | Date | Wed, 23 May 2018 09:14:33 +0300 |
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On 05/23/2018 07:00 AM, Takashi Sakamoto wrote: > Hi, > > On May 14 2018 15:27, Oleksandr Andrushchenko wrote: > > diff --git a/sound/xen/xen_snd_front_alsa.c > b/sound/xen/xen_snd_front_alsa.c > > new file mode 100644 > > index 000000000000..5041f83e98d2 > > --- /dev/null > > +++ b/sound/xen/xen_snd_front_alsa.c > > ... > > +/* > > + * FIXME: The mmaped data transfer is asynchronous and there is no > > + * ack signal from user-space when it is done. This is the > > + * reason it is not implemented in the PV driver as we do need > > + * to know when the buffer can be transferred to the backend. > > + */ > > ... > > In ALSA PCM interface v2.0.14 or later, SNDRV_PCM_INFO_SYNC_APPLPTR is > available. This flag express that userspace applications are expected to > call ioctl(2) with 'SNDRV_PCM_IOCTL_SYNC_PTR' even if they oprate to > memory mapped page frames for PCM samples. For detail, please refer to a > commit 42f945970af9 ('ALSA: pcm: Add the explicit appl_ptr sync > support')[1]. > > As a supplement, please refer to below commits: > * 4b671f577474 ('ALSA: pcm: Add an ioctl to specify the supported > protocol version')[2] > * b602aa8eb1a0 ('ALSA: pcm: Disable only control mmap for explicit > appl_ptr sync')[3] > > Alsa-lib v1.1.5 or later supports this flag and existent applications > can run transparently. > > For developers, a tracepoint may be useful: > * fccf53881e9b ('ALSA: pcm: add 'applptr' event of tracepoint')[4] > > For your information. > > [1] > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=42f945970af9 > [2] > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=4b671f577474 > [3] > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b602aa8eb1a0 > [4] > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=fccf53881e9b > Oh, this is very useful, thank you so much for such a detailed description. I'll take a close look at the above and see if Xen sound driver can benefit from this. > > Regards > > Takashi Sakamoto Thank you very much, Oleksandr
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