Re: [PATCH 08/11] MTD: m25p80: Add option to limit SPI transfer size.

Vinod Koul
2015-07-22T04:49:25Z

On Tue, Jul 21, 2015 at 10:14:11AM +0200, Michal Suchanek wrote:
> > Or alternatively we could publish the limitations of the channel using
> > capabilities so SPI knows I have a dmaengine channel and it can transfer max N
> > length transfers so would be able to break rather than guessing it or coding
> > in DT. Yes it may come from DT but that should be dmaengine driver rather
> > than client driver :)
> >
> > This can be done by dma_get_slave_caps(chan, &caps)
> >
> > And we add max_length as one more parameter to existing set
> >
> > Also all this could be handled in generic SPI-dmaengine layer so that
> > individual drivers don't have to code it in
> >
> > Let me know if this idea is okay, I can push the dmaengine bits...
>
> It would be ok if there was a fixed limit. However, the limit depends
> on SPI slave settings. Presumably for other buses using the dmaengine
> the limit would depend on the bus or slave settings as well. I do not
> see a sane way of passing this all the way to the dmaengine driver.
I don't see why this should be client (SPI) dependent. The max length
supported is a dmaengine constraint, typically flowing from max
blocks/length it can transfer. Know this limit can allow clients to split
transfers.

--
~Vinod
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