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

[Masahiro Yamada]

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.

-- 
Best Regards
Masahiro Yamada