sdhci-tegra and power-gpios

sdhci-tegra and power-gpios

[Chris Ball]

Hi Stephen, tegra folks,

sdhci-tegra uses a power-gpios property in the DT:

        sdhci@c8000400 {
                status = "okay";
                cd-gpios = <&gpio 69 0>; /* gpio PI5 */
                wp-gpios = <&gpio 57 0>; /* gpio PH1 */
                power-gpios = <&gpio 70 0>; /* gpio PI6 */
                bus-width = <4>;
        };

which it turns on at probe-time in the driver:

        plat->power_gpio = of_get_named_gpio(np, "power-gpios", 0);
        ...
	if (gpio_is_valid(plat->power_gpio)) {
		rc = gpio_request(plat->power_gpio, "sdhci_power");
		if (rc) {
			dev_err(mmc_dev(host->mmc),
				"failed to allocate power gpio\n");
			goto err_power_req;
		}
		gpio_direction_output(plat->power_gpio, 1);
	}

and then leaves on forever.  Seems like this should instead be a fixed
regulator (vmmc-supply) -- the MMC core would handle powering it up and
down as needed, and it's cleaner to let the regulator subsystem handle
power changes like this.  It might save you some power, too.

It's quite easy to set up a regulator and attach it to an MMC node:

        vmmc1: fixedregulator@0 {
                compatible = "regulator-fixed";
                regulator-name = "fixed-supply";
                regulator-min-microvolt = <2200000>;
                regulator-max-microvolt = <2200000>;
                gpio = <&gpio 70 0>; /* gpio PI6 */
                startup-delay-us = <70000>;
                vin-supply = <&parent_reg>;
        };
..
        sdhci@c8000400 {
                status = "okay";
                cd-gpios = <&gpio 69 0>; /* gpio PI5 */
                wp-gpios = <&gpio 57 0>; /* gpio PH1 */
		vmmc-supply = <&vmmc1>;
                bus-width = <4>;
        };

Any interest in making this change?  I've asked other drivers
(sdhci-pxav3 and sdhci-spear) to do the same thing (although
they hadn't merged their use of power-gpios yet and tegra has).

Thanks,

- Chris.
-- 
Chris Ball   <cjb-2X9k7bc8m7Mdnm+yROfE0A@public.gmane.org>   <http://printf.net/>
One Laptop Per Child

Re: sdhci-tegra and power-gpios

[Stephen Warren]

On 10/01/2012 09:15 AM, Chris Ball wrote:
> Hi Stephen, tegra folks,
> 
> sdhci-tegra uses a power-gpios property in the DT:
> 
>         sdhci@c8000400 {
...
>                 power-gpios = <&gpio 70 0>; /* gpio PI6 */
...
> It's quite easy to set up a regulator and attach it to an MMC node:
...
>         sdhci@c8000400 {
...
> 		vmmc-supply = <&vmmc1>;
...
> Any interest in making this change?

Yes, it's certainly something we should be doing. Most Tegra boards will
only have all the regulators defined in device tree for the first time
in kernel 3.7, and so we've been holding off making any of the client
nodes use regulators because of that. Now that we have all the
regulators defined, I do hope we will quickly move to using them for
SDHCI. Pavan (now CC'd) will hopefully be doing this.