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

[vinod.koul@intel.com (Vinod Koul)]

On Mon, Oct 07, 2013 at 05:45:22PM +0200, Guennadi Liakhovetski wrote:
> 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.
No that would be very wrong thing to do behind clients back. Suppose you got a
trasaction which returned error irq and it was generated one half of the
requested transfer was done. Redoing the entrie transaction wont be right!

So I think you need to let client know the error status.

But again, is this usage fiarly common?

--
~Vinod