[RFC] dmaengine/dma_slave: add context parameter to prep_slave_sg callback

[Vinod Koul]

On Wed, 2012-02-01 at 12:58 +0100, Guennadi Liakhovetski wrote:
> > The two things are completely orthogonal and shouldn't be clubbed.
> > For your issue we need a separate debate on how to solve this... I am
> > open to ideas...
> 
> Well, I'm not sure whether they are necessarily always orthogonal, they 
> don't seem so in my case at least. We definitely can use our approach - 
> configure the channel during allocation. I _think_ we could also perform 
> the configuration on a per-transfer basis, during the prepare stage, as 
> this RFC is suggesting, but that definitely would require reworking the 
> driver somewhat and changing the concept. The current concept is a fixed 
> DMA channel allocation to slaves for as long as the slave is using DMA. 
> This is simpler, avoids some overhead during operation and fits well with 
> the dmaengine PRIVATE channel concept. So, given the choice, we would 
> prefer to perform the configuration during channel allocation.
> 
> Maybe there are cases, where the driver absolutely needs this additional 
> information during allocation, in which case my proposal would be the only 
> way to go for them.
what are you trying to address, sending controller specific information
at allocation or the channel allocation itself. I kind of sense both.
But apprach here is discussed is to pass paramters which are required
for each transfer, not static for a channel, hence the additional
controller specific parameter in respective prepare. 
> 
> I'll post an RFC soon - stay tuned:-) 
Patch is always the best idea :-)

-- 
~Vinod