Re: [PATCH RFC 2/3] mmc: sdhci-omap: Add using external dma

[Chunyan Zhang]

On Tue, 6 Nov 2018 at 20:51, Arnd Bergmann <arnd@xxxxxxxx> wrote:
>
> On 11/5/18, Kishon Vijay Abraham I <kishon@xxxxxx> wrote:
> > On 05/11/18 8:46 AM, Chunyan Zhang wrote:
> >>
> >> +    sdhci_switch_extdma(host, true);
> >
> > A number of devices using sdhci-omap supports ADMA. So switching to
> > external
> > DMA shouldn't be unconditional.
> >
> > IMHO sdhci.c should see if the device supports ADMA or SDMA. If not it
> > should
> > try switching to external DMA and if external DMA too is not supported, it
> > should use PIO.
>
> What's the reasoning for preferring ADMA/SDMA over external DMA if
> both are supported?
>
> I'd expect that if the external DMA for some reason is worse than
> ADMA, we just wouldn't list it in the DT at all, but if it's listed and
> ADMA also works, then the driver should try to use it before falling
> back to ADMA.

Thanks Arnd and Kishon, let's see what Andrian and Ulf would suggest,
and then I will address in next version of patchset.

Thanks again,
Chunyan

>
>        Arnd