Re: [PATCH 1/3] mmc: add support for power-on sequencing through DT

[Olof Johansson <olof-nZhT3qVonbNeoWH0uzbU5w@public.gmane.org>]

On Mon, Jan 20, 2014 at 10:58 AM, Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org> wrote:
> On Monday 20 January 2014, Olof Johansson wrote:
>>
>> +Card power and reset control:
>> +The following properties can be specified for cases where the MMC
>> +peripheral needs additional reset, regulator and clock lines. It is for
>> +example common for WiFi/BT adapters to have these separate from the main
>> +MMC bus:
>> +  - card-reset-gpios: Specify GPIOs for card reset (reset active low)
>> +  - card-external-vcc-supply: Regulator to drive (independent) card VCC
>> +  - clock with name "card_ext_clock": External clock provided to the card
>
> I wonder whether the reset line should use the generic reset controller binding
> rather than the gpio binding. There has been a recent discussion about a
> gpio-reset driver, which should generalize this at the reset level, and
> it would make it possible to use reset controllers that are not gpio driven.
> In general, any gpio can be used as a reset, but not every reset line can
> be a gpio. I don't know whether anyone would use an internal reset-controller
> for an external SDIO chip though, so maybe your approach is sufficient.

I'd expect most usage of this to be through gpios, since we're talking
about external independent modules here. I would prefer not to bring
in the reset controller stuff here -- it just adds another layer of
abstraction that seems unnecessary.

I would prefer if the reset framework was contained to only be the
on-chip SoC IP block resets, etc, as originally intended.


-Olof
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