Hi Ian,
On Wed, Jul 12, 2017 at 04:28:19PM +0100, Ian Molton wrote:
> Hi folks,
>
> I'm working on a SDIO wifi card and I'm attempting to figure out how on
> earth voltage regulation works for MMC slots.
>
> The mmc host is an imx6ul
>
> In its DT, it has the following:
>
> &usdhc1 {
> #address-cells = <1>;
> #size-cells = <0>;
> pinctrl-names = "default", "state_100mhz", "state_200mhz";
> pinctrl-0 = <&pinctrl_usdhc1>;
> pinctrl-1 = <&pinctrl_usdhc1_100mhz>;
> pinctrl-2 = <&pinctrl_usdhc1_200mhz>;
> no-1-8-v;
> keep-power-in-suspend;
> enable-sdio-wakeup;
> vmmc-supply = <®_sd1_vmmc>;
> non-removable;
> status = "okay";
> }
>
> Its working, however I cannot seem to get it to turn off power to the
> slot. I would expect that if the card is probed and no driver wants to
> attach, the slot can be turned off.
>
I don't think your regulator will be turned off automatically, you may rely on
your bootloader to do it. MMC core will turn it on. I let you dig into the
code. Regulator state is updated when calling set_ios() depending on
ios power_mode.
> cat /sys/class/regulator/regulator.5/state tells me the regulator is
> enabled, and num_users is 1
>
> whats really puzzling me is that nowhere in the code does git grep show
> *any* attempt to look up a regulator called vmmc-supply, or a dt
> property with the same name. Unless I'm being blind...
>
Have a look to of_get_regulator.
Regards
Ludovic
> I assume the of regulator code is looking up the parent device and
> enabling the regulator for me, but then I cannot see how the MMC core /
> host driver might control the regulator.
>
> Is this all as it is expected to be?
>
> What I'd like is for an attempt to load the wifi module to cause the MMC
> host to turn on the power and let the card try to re-enumerate/probe,
> and for driver unloading to cause the card to get turned off again.
>
> I cant see a good way to toggle slot power from userspace either -
> although I may just be missing this?
>
> TIA for comments,
>
> -Ian
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