[PATCH/RFC] board: amlogic: Fix Odroid-C4 SD card reboot issue

[Marek Szyprowski]

Hi Neil,

On 18.12.2020 10:24, Neil Armstrong wrote:
> On 18/12/2020 10:11, Marek Szyprowski wrote:
>> On 18.12.2020 09:36, Neil Armstrong wrote:
>>> On 17/12/2020 10:06, Marek Szyprowski wrote:
>>>> For the proper reboot Odroid C4 board requires to switch TFLASH_VDD_EN
>>>> pin to the input (high impedance?) mode, otherwise the board is stuck
>>>> in the middle of loading early stages of the bootloader from SD card.
>>> Did you try taking the regulator-tflash_vdd and doing a disable/enable sequence
>>> to reset the card ?
>>>
>>> The GPIOAO_3 has a default pull-up, so I don't see why moving it to input could change
>>> anything.
>>>
>>> So maybe simply doing a 0->1 transition could do the same, using the regulator
>>> would be much better.
>>>
>>> Can't we add "shutdown" or equivalent method to  the mmc driver that could do this
>>> directly with the vdd regulator ?
>> Yes, I've tried all combinations of playing this that GPIO and regulator
>> that came to my mind. Switching pin to the input is the only one I've
>> found working.
> Thanks for the dumps !
>
> Could you try switching the tflash_vdd to opendrain like :
>
> --->8---
>
> --- a/arch/arm/dts/meson-sm1-odroid-c4.dts
> +++ b/arch/arm/dts/meson-sm1-odroid-c4.dts
> @@ -52,7 +52,7 @@
>                  regulator-min-microvolt = <3300000>;
>                  regulator-max-microvolt = <3300000>;
>
> -               gpio = <&gpio_ao GPIOAO_3 GPIO_ACTIVE_HIGH>;
> +               gpio = <&gpio_ao GPIOAO_3 GPIO_OPEN_DRAIN>;
>                  enable-active-high;
>                  regulator-always-on;
>          };
>
> --->8---
>
> This should leave the pin in input to achieve high state, and solve the issue.
>
Right, this fixed the issue! Thanks!

Do you want me to submit it as a patch to uboot and mainline Linux 
kernel or do you want to handle it by yourself?

Best regards

-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland