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

On Wed, 2012-02-01 at 12:58 +0100, Guennadi Liakhovetski wrote:

quoted

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