FW: [alsa-devel] [PATCH 2/4] ASoC: mmp: add audio dma support

-----Original Message-----
From: Russell King - ARM Linux [mailto:linux at arm.linux.org.uk]
Sent: Friday, May 25, 2012 5:43 PM
To: zhangfei gao
Cc: Vinod Koul; alsa-devel at alsa-project.org; linux-arm-kernel at lists.infradead.org; Eric Miao; Leo Yan; Mark Brown; Haojian Zhuang; alsa-devel at vger.kernel.org; Qiao Zhou; Zhangfei Gao; Liam Girdwood; Chao Xie
Subject: Re: [alsa-devel] [PATCH 2/4] ASoC: mmp: add audio dma support

On Fri, May 25, 2012 at 04:47:20PM +0800, zhangfei gao wrote:

quoted

Do you mean at open time, like snd_dmaengine_pcm_open.
The channel resource is limited and better get dynamically.
As a ?result the pcm_new and preallocate already called before.

This is where dealing with slave DMA channels in a virtualized setup
becomes a far better solution than trying to assign a particular
physical channel at request time.

What we may wish to think about is having a way for slave drivers to
assert to DMA engine the priority of a channel, which they can change
dynamically according to what they're doing. ?Eg, an ALSA driver would
leave the channel low priority while it's not expecting to be used, but
as soon as we see the prepare call, set it to high priority.

The DMA engine driver could use that to decide to assign a physical
channel to the virtual channel, so that DMA can start as soon as
possible even with other activity on the DMA engine.

However, I've yet to see any setup where the number of physical DMA
channels available exceeds the number of actual _simultaneous_ users.
Even with the five channels on SA11x0 shared between 12? peripherals,
with my DMA engine driver I've only seen one or two physical channels
being used simultaneously.

I can understand that the virtual channel and physical channel. But i
do not know that why you said that buf->dev.dev uses the right device,
and we don't need set the coherent_mask and dma_mask. As i understand
that buf->dev.dev should be the audio device, so why do you said that
it is the dma engine device?