At Wed, 14 Nov 2007 17:43:21 +0530, Pharaoh . wrote:
On Nov 14, 2007 1:44 PM, Takashi Iwai tiwai@suse.de wrote:
At Wed, 14 Nov 2007 00:12:07 +0530, Pharaoh . wrote:
Hi,
I am trying to use snd_pcm_lib_preallocate_pages_for_all() on an arm
based
platform for preallocating the DMA buffer. I am using it as
snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV, NULL, 64 * 1024, 64 * 1024);
since I dont know what should be passed as the 3'rd param. I tried
passing
my device pointer i.e. card->dev after correctly populating it but I get an error as 'DMA coherent mask in not
set'
and buffer is not allocated.
For ARM, avoid the present buffer-preallocation and mmap functions in ALSA core. Instead you can allocate the buffers directly via normal dma_alloc_coherent() in your driver. And, mmap it via dma_mmap_coherent() by defining the own mmap callback for PCM ops.
See other arm/* drivers for rerecence.
Takashi
Yes, I am using my own buffer preallocation scheme now. I allocate a 128K buffer using dma_alloc_coherent in probe and free it only in remove i.e. at rmmod time.
I dont think keeping a huge buffer like this till driver removal is a good idea but when I allocate/deallocate it in hw_params/hw_free respectively, it is causing fragmentation and sometimes the allocation fails. Do you think anything better can be done?
Unfortuantely, no other way, so far. It's the only way that a driver can do -- keeping the large chunk as long as it needs.
Takashi