Takashi Iwai wrote:
At Wed, 16 Jan 2008 09:17:57 -0600, Timur Tabi wrote:
My 8610 ASoC driver has this:
static const struct snd_pcm_hardware fsl_dma_hardware = {
.info = SNDRV_PCM_INFO_INTERLEAVED,
This means that MMAP is not enabled.
I understand what MMAP is, but not from an ALSA driver perspective. If I change the above line to this:
.info = SNDRV_PCM_INFO_INTERLEAVED | SNDRV_PCM_INFO_MMAP | SNDRV_PCM_INFO_MMAP_VALID,
what does ALSA do differently? Do I need to define any new functions? From an application perspective, what is different?
It means that the driver supports mmap access to the PCM buffer.
In some cases, you need to implement a proper mmap callback. For example, when the coheret (dma) pages are allocated via dma_alloc_coherent and used for the PCM buffer, you need mmap callback for ARM, at least because the default mmap handler in the PCM core doesn't work for ARM. In this case, prepare your own mmap callback and pass it to pcm ops. It should call simply dma_mmap_coherent() appropriately.
The default mmap handler in the PCM core is snd_pcm_default_mmap()?
How can I know whether this function works? Can I just add those two flags to my .info line, and then .... ? Is there an ALSA mmap test utility?
Also, does DMIX need MMAP support?
Yes, mandatory.
So just to be clear: the fact that I do *not* have "SNDRV_PCM_INFO_MMAP | SNDRV_PCM_INFO_MMAP_VALID" defined in snd_pcm_hardware.info is the reason why I get this error message:
root@MPC8610HPCD:/home/demo_files/mp3# alsaplayer -o alsa -q -F 48000 -d plug:dmix ./527182737.mp3 & [1] 3224 root@MPC8610HPCD:/home/demo_files/mp3# ALSA lib pcm_direct.c:874:(snd_pcm_direct_initialize_slave) slave plugin does not support mmap interleaved or mmap noninterleaved access ALSA lib pcm_dmix.c:878:(snd_pcm_dmix_open) unable to initialize slave snd_pcm_open: Invalid argument (plug:dmix) Failed to initialize plugin! ...