Re: [PATCH] mmc: mmci: stm32: handle mmc power up

[Marek Vasut <marex@nabladev.com>]

On 11/11/26 12:45 PM, Ulf Hansson wrote:

Hello Ulf,

>>>> -       if (ios.power_mode == MMC_POWER_OFF) {
>>>> +       if (ios.power_mode == MMC_POWER_OFF ||
>>>> +           ios.power_mode == MMC_POWER_UP) {
>>>>                   /* Only a reset could power-off sdmmc */
>>>>                   reset_control_assert(host->rst);
>>>>                   udelay(2);
>>>
>>> What exactly will this reset?
>> The controller.
> 
> Okay, I see.
> 
> In that case, this reset also makes us reset preceding updates to any
> other registers, for example the clock register. I would not recommend
> doing that here, but perhaps there is no better option.

Does that pose a problem in the MMC_POWER_OFF/UP state ? I agree this 
would pose a problem in the MMC_POWER_ON state, but here the card is not ON.

> If I may I suggest an alternative solution, perhaps we can manage this
> in the ->runtime_resume() callback instead. If the power_mode ==
> MMC_POWER_OFF, perhaps do this reset there instead? Would that work?
> 
> Anothing thing that caught my eyes was the MCI_STM32_PWR_CYC bit that
> gets written at MMC_POWER_OFF. This bit becomes cached in
> host->pwr_reg, hence it's also rewritten at MMC_POWER_ON. Is that
> intentional?
I _think_ so, this seems to be used to power cycle the card.