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

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Sun, Jan 19, 2014 at 07:56:53PM -0800, Olof Johansson wrote:
> diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt b/Documentation/devicetree/bindings/mmc/mmc.txt
> index 458b57f..962e0ee 100644
> --- a/Documentation/devicetree/bindings/mmc/mmc.txt
> +++ b/Documentation/devicetree/bindings/mmc/mmc.txt
> @@ -5,6 +5,8 @@ these definitions.
>  Interpreted by the OF core:
>  - reg: Registers location and length.
>  - interrupts: Interrupts used by the MMC controller.
> +- clocks: Clocks needed for the host controller, if any.
> +- clock-names: Goes with clocks above.
>  
>  Card detection:
>  If no property below is supplied, host native card detect is used.
> @@ -30,6 +32,15 @@ Optional properties:
>  - cap-sdio-irq: enable SDIO IRQ signalling on this interface
>  - full-pwr-cycle: full power cycle of the card is supported
>  
> +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
> +

This looks good.  I can connect the wifi/bt power control to a regulator,
and give that as the card-external-vcc-supply property.  I can specify
the WIFI/BT resets for card-reset-gpios.

So far so good.  Now, what about this external oscillator which has its
own separate power control.  My immediate thought is that this can be
specified via card_ext_clock - I would simply need to declare a fixed-rate
clock with either a regulator (power switch) controlled via a gpio (which
would probably be closer to the hardware) or a gpio as an enable... ah,
that requires me to write a common clock driver for that bit since this
is currently not modelled by CCF...

-- 
FTTC broadband for 0.8mile line: 5.8Mbps down 500kbps up.  Estimation
in database were 13.1 to 19Mbit for a good line, about 7.5+ for a bad.
Estimate before purchase was "up to 13.2Mbit".