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| author | Takashi Sakamoto <o-takashi@sakamocchi.jp> | 2016-12-11 20:31:38 +0900 |
|---|---|---|
| committer | Takashi Iwai <tiwai@suse.de> | 2016-12-12 22:36:29 +0100 |
| commit | d008e1ac203dde67838effe43bd512d38bd92f24 (patch) | |
| tree | 030ead7a8115974609f4f3368d90c3f783a33b70 | |
| parent | 60b68cb47ed5da9b3c0adde04c69df2649feafe8 (diff) | |
| download | alsa-lib-d008e1ac203dde67838effe43bd512d38bd92f24.tar.gz | |
pcm: fix wrong document references to PCM APIs which perform direct memory access with frame copying
In a design of ALSA PCM interface, for PCM frame transmission to/from
kernel space, applications can select from two options; direct memory access
or ioctl(2). Available options are decided depending on device capacity and
machine architecture. Applications can get available options by the first
entry of 'struct snd_pcm_hw_params.masks'.
When the mask includes 'SNDRV_PCM_ACCESS_MMAP_xxx', applications can use
direct memory access. For this use case, userspace library has two types
of PCM API. One is to expose a pointer over the memory to start
reading/writing PCM frames. Another is to copy PCM frames between the
memory and a given buffer.
Current documentation includes wrong references to these APIs to describe
their advantages/disadvantages. This confuses application developers
because the references indicate PCM APIs to execute ioctl(2) operation to
read/write PCM frames.
This commit fixes the bug.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
| -rw-r--r-- | src/pcm/pcm.c | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/src/pcm/pcm.c b/src/pcm/pcm.c index f2ca02b5..0cf740f8 100644 --- a/src/pcm/pcm.c +++ b/src/pcm/pcm.c @@ -260,8 +260,9 @@ If you like to use the compatibility functions in mmap mode, there are read / write routines equaling to standard read / write transfers. Using these functions discards the benefits of direct access to memory region. See the #snd_pcm_mmap_readi(), -#snd_pcm_writei(), #snd_pcm_readn() -and #snd_pcm_writen() functions. +#snd_pcm_mmap_writei(), #snd_pcm_mmap_readn() +and #snd_pcm_mmap_writen() functions. These functions use +#snd_pcm_areas_copy() internally. \section pcm_errors Error codes |