[U-Boot] [PATCH 5/6] mmc: move some SDHCI related options to Kconfig

[Tom Rini]

On Wed, Dec 07, 2016 at 06:04:21PM +0900, Masahiro Yamada wrote:
> Hi Tom
> 
> 2016-12-06 4:10 GMT+09:00 Tom Rini <trini at konsulko.com>:
> > On Sun, Dec 04, 2016 at 10:23:13PM +0900, Masahiro Yamada wrote:
> >
> >> While I moved the options, I also renamed them so that they are all
> >> prefixed with MMC_SDHCI_.
> > [snip]
> >> diff --git a/drivers/mmc/Kconfig b/drivers/mmc/Kconfig
> >> index 8e9fa2d..4785d71 100644
> >> --- a/drivers/mmc/Kconfig
> >> +++ b/drivers/mmc/Kconfig
> >> @@ -132,6 +132,68 @@ config MMC_SDHCI
> >>
> >>         If unsure, say N.
> >>
> >> +config MMC_SDHCI_SDMA
> >> +     bool "Support SDHCI SDMA"
> >> +     depends on MMC_SDHCI
> >> +     help
> >> +       This enables support for the SDMA (Single Operation DMA) defined
> >> +       in the SD Host Controller Standard Specification Version 1.00 .
> >
> > I think this should be a default y.
> 
> No.
> 
> After my conversion,
> 
> masahiro at pug:~/workspace/u-boot/configs$ git grep CONFIG_MMC_SDHCI=y | wc
>      54      54    2306
> masahiro at pug:~/workspace/u-boot/configs$ git grep CONFIG_MMC_SDHCI_SDMA=y | wc
>      21      21     995
> 
> 
> So, SDMA is disabled for more than half of boards with SDHCI driver.
> 
> 
> I know one more reason that we should not enable option by default.
> 
> SDMA is so old that it only supports 32 bit physical address.
> 
> U-Boot uses the tail of memory area as work RAM.
> 
> If SDMA is enabled on 64bit boards, MMC does not work
> because the controller cannot read EXT-CSD data.
> 
> Given increasing ARMv8 boards,
> we want to use ADMA(2), but it is not supported in U-Boot.
> 
> Anyway, I believe SDMA does not deserve default.

OK, thanks, agreed!

-- 
Tom
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