From mboxrd@z Thu Jan  1 00:00:00 1970
From: Holger Schurig <holgerschurig@gmail.com>
Subject: BUG 4.4rc-4: wrong eMMC signaling voltage reported
Date: Wed, 09 Dec 2015 15:53:06 +0100
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Hi,

I have an i.MX6Q based system that cannot provide 1.8V voltage towards
the eMMC. But Linux 4.4-rc4 reports 1.8V for the eMMC, but this is
impossible. Neither my hardware allows this, nor does the DT say it.

root@imx6q:/sys/kernel/debug# cat mmc1/ios
clock:		52000000 Hz
actual clock:	49500000 Hz
vdd:		21 (3.3 ~ 3.4 V)
bus mode:	2 (push-pull)
chip select:	0 (don't care)
power mode:	2 (on)
bus width:	3 (8 bits)
timing spec:	8 (mmc DDR52)
signal voltage:	0 (1.80 V)
driver type:	0 (driver type B)

My device tree however tells that I don't have 1.8V:

/* this is the built in eMMC */
&usdhc4 {
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_usdhc4>;
	bus-width = <8>;
	non-removable;
	vmmc-supply = <&reg_3p3v>;
	max-frequency = <198000000>;
	no-1-8-v;
	status = "okay";
};




Fun fact: for the SDCARD things are correctly reported:

root@imx6q:/sys/kernel/debug# cat mmc1/ios
clock:		36000000 Hz
actual clock:	33000000 Hz
vdd:		21 (3.3 ~ 3.4 V)
bus mode:	2 (push-pull)
chip select:	0 (don't care)
power mode:	2 (on)
bus width:	2 (4 bits)
timing spec:	2 (sd high-speed)
signal voltage:	0 (3.30 V)
driver type:	0 (driver type B)

And here my device tree excerpt:

/* this is the SDCARD slot */
&usdhc2 {
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_usdhc2>;
	cd-gpios = <&gpio1 2 GPIO_ACTIVE_LOW>;
	wp-gpios = <&gpio1 4 GPIO_ACTIVE_HIGH>;
	vmmc-supply = <&reg_3p3v>;
	max-frequency = <36000000>;
	no-1-8-v;
	status = "okay";
};