[U-Boot] [PATCH 1/3] samsung: board: support eMMC reset using DT

[Joonyoung Shim]

Hi,

On 01/09/2015 01:21 PM, Jaehoon Chung wrote:
> On 01/09/2015 08:23 AM, Sjoerd Simons wrote:
>> On Thu, 2015-01-08 at 14:44 +0900, Joonyoung Shim wrote:
>>> Some exynos boards require special handling of SD4_nRESET_OUT line for
>>> eMMC memory to perform complete reboot e.g. Odroid X2/U3/XU3 boards.
>>>
>>> This will support eMMC reset using DT from reset_misc of samsung common
>>> board file and each board files can support eMMC reset on non DT case.
>>>
>>> Signed-off-by: Joonyoung Shim <jy0922.shim at samsung.com>
>>
>>> diff --git a/doc/device-tree-bindings/exynos/emmc-reset.txt b/doc/device-tree-bindings/exynos/emmc-reset.txt
>>> new file mode 100644
>>> index 0000000..e48e508
>>> --- /dev/null
>>> +++ b/doc/device-tree-bindings/exynos/emmc-reset.txt
>>> @@ -0,0 +1,15 @@
>>> +* Samsung eMMC reset
>>> +
>>> +Some exynos boards require special handling of SD4_nRESET_OUT line for eMMC
>>> +memory to perform complete reboot.
>>
>> Nitpick, on XU3 the line you apparently need to twiddle is
>> SD0_nRESET_OUT.
>>

Then, i think it's better to omit "SD4_".

>> Is this type of usage of this pin specific to the Odroid Exynos boards
>> or potentially on more boards? (Sorry for the simple questions, but my
>> exynos documentation just says the line exists not what its intended
>> usage is). 
> 
> In case of Exynos4, eMMC can be used with sdhci controller or dw-mmc controller.
> So Pin name should be used to SD0 or SD4.
> 
> But Exynos5 is only supported the dw-mmc controller.
> (So eMMC is used pin-name as "SD0".)
> 

I can find only "SD_4_nRESET_OUT" from exynos4412 user manual and only
"SD_0__nRESET_OUT" from exynos5422 user manual.

> Best Regards,
> Jaehoon Chung
>>
>> Fwiw, I did a quick check in the linux code and it doesn't seem to be
>> using those pins for currently for any boards. However my X2 does
>> successfully reset/reboot in u-boot and linux, so it seems optional
>> there. The XU3 does fail to reset itself, so it seems required for that
>> board.
>>

I checked upstream u-boot and hardkernel u-boot and i found codes to
reset eMMC using gpio.

upstream u-boot: reset_misc() of board/samsung/odroid/odroid.c
hardkernel u-boot: reset_cpu() of arch/arm/cpu/armv7/exynos/reset.c

Thanks.