[alsa-devel] SNDRV_PCM_INFO_MMAP - what do I need for it?
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?
Also, does DMIX need MMAP support?
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.
Also, does DMIX need MMAP support?
Yes, mandatory.
Takashi
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! ...
Timur Tabi wrote:
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?
Ok, I think aplay can do this.
I ran this command:
aplay -Dhw:0,0 -f S16_BE -M -r 48000 -c 2 15.raw
and I got this error:
aplay: set_params:852: Access type not available
so I modified my .info line and added those two macros. When I run "aplay -M", it plays the file fine.
Does this mean that my one-line change has added mmap support to my driver, and dmix should now work?
On Wed, 16 Jan 2008, Timur Tabi wrote:
Takashi Iwai wrote:
At Wed, 16 Jan 2008 09:17:57 -0600, Timur Tabi wrote:
.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?
You can use the -M option with arecord and aplay too see if mmap works. You need to actually hear/record sound to know, just getting no errors isn't enough.
The default mmap hander will work if you used ALSA to allocate the DMA buffer. If you didn't, for example the cx88-alsa and bt87x drivers use vmalloc(), then you need to write your own mmap handler. The handler I wrote for the previously mentioned drivers wasn't complex.
participants (3)
-
Takashi Iwai -
Timur Tabi -
Trent Piepho