[Linux-stm32] [PATCH] [RFC] mmc: mmci: Add support for probing bus voltage level translator

[Yann GAUTIER]

On 1/13/21 12:52 PM, Marek Vasut wrote:
> On 1/13/21 12:38 PM, Ulf Hansson wrote:
> [...]
>>>>>    static int mmci_of_parse(struct device_node *np, struct mmc_host 
>>>>> *mmc)
>>>>>    {
>>>>>           struct mmci_host *host = mmc_priv(mmc);
>>>>> @@ -1913,7 +1973,7 @@ static int mmci_of_parse(struct device_node 
>>>>> *np, struct mmc_host *mmc)
>>>>>           if (of_get_property(np, "st,neg-edge", NULL))
>>>>>                   host->clk_reg_add |= MCI_STM32_CLK_NEGEDGE;
>>>>>           if (of_get_property(np, "st,use-ckin", NULL))
>>>>> -               host->clk_reg_add |= MCI_STM32_CLK_SELCKIN;
>>>>> +               mmci_probe_level_translator(mmc);
>>>>
>>>> I think you can make this change bit less invasive. Rather than having
>>>> to shuffle code around in ->probe(), I suggest you call
>>>> mmci_probe_level_translator() outside and after mmci_of_parse() has
>>>> been called.
>>>>
>>>> In this way, you can also provide mmci_probe_level_translator() with a
>>>> struct mmci_host *, rather than having to pick it up from
>>>> mmc_priv(mmc), if you see what I mean.
>>>>
>>>> Of course, this also means in mmci_probe_level_translator() you will
>>>> have to check if MCI_STM32_CLK_SELCKIN has been set, and if not then
>>>> do an early return.
>>>
>>> Testing the translator presence when checking whether its enabled in DT
>>> seems like the right place, but that's really just an implementation 
>>> detail.
>>>
>>> I am more interested in knowing whether adding
>>> mmci_probe_level_translator() is even acceptable in the first place. 
>>> Is it ?
>>
>> Honestly, I don't know.
>>
>> I think I need to defer that question to Linus Walleij. And of course,
>> it would be nice to get the opinion from Ludovic as well.
> 
> Good, that's what I was hoping for too.

Hi,

Ludovic is out of office this week.

The feature of detecting a level translator seems to be quite generic, 
and not dedicated to MMCI driver or the ST dedicated code, and with new 
st,* properties. It may be in generic mmc code. But I'll let Linus 
comment about that.

I also wonder if this HW detection should be done in kernel, or if it 
should be done in Bootloader. But it may be more complex, to add the 
st,use_ckin in kernel DT if bootloader detects this translator.


Regards,
Yann

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