Re: [PATCH v3 8/9] spi: rockchip: modify DMA max burst to 1

[Shawn Lin]

On 2015/9/4 1:45, Mark Brown wrote:
> On Thu, Sep 03, 2015 at 09:41:43PM +0800, Shawn Lin wrote:
> > On 2015/9/3 20:54, Mark Brown wrote:
>
> > > If this is a quirk of the DMA controller why is it being fixed with a
> > > property specific to the SPI controller?  Can't the DMA controller just
> > > override the burst size?
>
> > Cool...that's a good question. Actually DMA controller can't do that since
> > block peripheral controller(e.g sd/emmc, they always access data by
> > block-512Bytes.) can't meet the case. So It's hard for dma controller know
> > who is the caller, and what should be done.
>
> You could take a guess based on request size, but that's going to be a
> bit error prone I imagine.

yes, not always cover all cases.

> > The only thing dma controller can do is avoid to execute DMAFLUSHP on its
> > own. But how about peripheral controller trigger non-multiple access? So
> > that's what I mentioned on covery letter that we should do "broken things"
> > for both dma controller and some peripherals.
>
> The other thing it could do is provide the information out via some
> internal Linux API which the drivers could query instead of directly
> having a DT property in each client driver.  That way at least the DT
> only needs the quirk in one place even if the clients need to handle it
> individually.

Good idea. Thanks, Mark.

>


--
Best Regards
Shawn Lin

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