Hi,
On Jun 21 2017 00:33, Takashi Iwai wrote:
Hi,
this is a patchset for the issues we've discussed recently lengthily, the explicit sync of appl_ptr by disabling the control mmap. The first patch achieves it for a driver setting the new INFO flag.
The second patch is for a generic ABI extension I wanted to implement for long time. It allows user-space reporting its supporting protocol version, so that the kernel can behave differently. It's especially useful for extending the ABI struct to use the reserved bits.
The third patch is the optimization by the second patch; it simply skips the previous workaround when the user-space declares itself being new enough to support the feature.
The corresponding alsa-lib patchset will follow in another thread.
thanks,
Takashi
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Takashi Iwai (3): ALSA: pcm: Add the explicit appl_ptr sync support ALSA: pcm: Add an ioctl to specify the supported protocol version ALSA: pcm: Limit the appl_ptr sync workaround only for old user-space
include/sound/pcm.h | 1 + include/uapi/sound/asound.h | 4 +++- sound/core/pcm_compat.c | 1 + sound/core/pcm_native.c | 28 ++++++++++++++++++++++++++++ 4 files changed, 33 insertions(+), 1 deletion(-)
I prefer this direction and support this patchset.
Reviewed-by: Takashi Sakamoto o-takashi@sakamocchi.jp Tested-by: Takashi Sakamoto o-takashi@sakamocchi.jp
However, when running with patched alsa-lib[1], due to a commit f8ff2f28ba49 ("ALSA: pcm: Skip ack callback without actual appl_ptr update")[2], callback functions in driver side for .ack are not called from ioctl handler in ALSA PCM core. When page frames for control data of PCM substream is mapped to VMA of the application, the application updates the value of pointer in the frame, then transfer the value via ioctl. Comparing these two values should be the same and ALSA PCM core skip the callback.
When considering about behaviour of old userland stuffs, it's not necessarily easy to reduce call frequency of the callback, mmm...
[1] http://mailman.alsa-project.org/pipermail/alsa-devel/2017-June/122066.html [2] https://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git/commit/sound...
Thanks
Takashi Sakamoto