[PATCH] DMA: extend documentation to provide more API details

[Guennadi Liakhovetski]

On Mon, 7 Oct 2013, Vinod Koul wrote:

> On Mon, Oct 07, 2013 at 05:28:37PM +0200, Guennadi Liakhovetski wrote:
> > > > > > > No, not something in the middle. I was thinking about
> > > > > > > 
> > > > > > > (1) cookie 1-3 are submitted
> > > > > > > (2) cookie 1 succeeds
> > > > > > > (3) a DMA error occurs, cookies 2-3 are discarded
> > > > > discarded using terminate_all right?
> > > > 
> > > > No, by the dmaengine driver as a part of the error processing.
> > > And how will that be done...?
> > 
> > Sorry, I meant - DMA descriptors with cookies #2 and #3 will be cancelled 
> > and recycled by the dmaengine driver. That's what you have to do, when 
> > processing DMA error IRQ.
> Well how do you that?

Mmmh, maybe I'm missing something, but isn't it a part of the common DMA 
processing? You get an error IRQ; on some DMAC types this means, that you 
have to reset the hardware, so, you perform whatever actions you have to 
do to reset the controller; you remove any descriptors from the pending 
queue; reinsert them into the free queue and let any clients run on a 
timeout. I don't think it would be a good idea to do anything more smart 
like trying to restart the current transfer or drop it and continue with 
the queue, because we don't know in what state the client hardware is, so, 
we can only let the client driver try to recover.

Thanks
Guennadi
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Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/