[alsa-devel] [PATCH 0/4] McBSP smart idle and DMA op mode updates for ASoC

[Eduardo Valentin]

On Wed, May 19, 2010 at 01:07:11PM +0200, Liam Girdwood wrote:
> On Wed, 2010-05-19 at 13:42 +0300, Eduardo Valentin wrote:
> > On Tue, May 18, 2010 at 10:13:10PM +0200, Liam Girdwood wrote:
> > > This series expands the OMAP mcbsp driver to support changing it's DMA operating
> > > mode and smart idle mode from client drivers. It's primarily aimed at lowering
> > > the power consumption for OMAP ASoC drivers by providing methods to gate clocks
> > > on the mcbsp interface at runtime.
> > > 
> > > I've also added a patch to remove the mcbsp DMA op mode sysfs set functionality.
> > > I think DMA op mode is very specific to the mcbsp client driver _only_ and
> > > shouldn't really be changed by userspace. Please let me know if you use this
> > > feature and I'll drop this patch.
> > 
> > Yeah, I'm not sure if that would be strong enough argument though. Unfortunately,
> > this dma op mode also couples with the usage of mcbsp internal buffer. Which in the very
> > end will mean a compromise between delay vs. pm, as you are probably aware.
> > 
> > So, letting userspace to toggle this mode will also mean they can choose between pm friendly
> > (op mode with frame and so on) or short delay friendly (element mode).
> > 
> > Of course, this might not be the best way of choosing it though.
> > 
> 
> The sysfs set interface implies userspace having knowledge of driver
> capabilities and configuration in order to safely toggle between the two
> DMA modes. Imo, the mcbsp client driver should be the only entity
> configuring it's DMA modes (in a safe manner) depending on the use case.


OK. That is fair enough. But it isn't clear in your patch series/description, how the client will
determine which use case to use. I understand your point and I agree with it. However, the way
it's being done here, it does not explain how the same issue will be handled after the removal of this
interface. That's my main concern.

> 
> Liam
> -- 
> Freelance Developer, SlimLogic Ltd
> ASoC and Voltage Regulator Maintainer.
> http://www.slimlogic.co.uk
>