Re: [PATCH 1/2] mmc: dw_mmc-exynos: add support for controlling emmc reset pin

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On 28 January 2015 at 16:23, Tobias Jakobi <liquid.acid@xxxxxxx> wrote:
> Ulf Hansson wrote:
>> On 28 January 2015 at 13:41, Tobias Jakobi <liquid.acid@xxxxxxx> wrote:
>>> Hello!
>>>
>>> Jaehoon Chung wrote:
>>>> mmc core supported to hw_reset function.
>>>> So i think we can use it. It's called at only initial time to clear the previous status.
>>>> But i think it can be called at reboot time. (it needs to implement codes.)
>>>> how about?
>>> I don't think that's going the work. The problem here is that depending
>>> on the board configuration, the eMMC might carry the bootloader. If the
>>> eMMC subsystem is not properly reset _during_ reboot, the board won't
>>> even start since no bootloader is found. So we don't even reach the
>>> point where the kernel does anything.
>>
>> I guess it depends on what's being done during the reboot sequence.
>>
>> The most proper thing would be to let the boot loader control the GPIO
>> to trigger the HW reset, but that would mean the boot loader need to
>> know about board specific configurations, such as which GPIO pin. So
>> maybe SOC vendors need to state what GPIO pin to use and don't leave
>> that as a configurable option.
> Not the bootloader, but the iROM code would have to do this, and as far
> as I know the iROM can't be modified. Or am I missing something here?

You are right! The "bootloader" can very likely be stored in ROM code.
That's why I also said the GPIO shouldn't be configurable. :-)

Kind regards
Uffe
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