AM3351: Output pullup/pulldown resistor

Sorry I forgot to mention that in Linux code we see that

Actually it is available in

include/dt-bindings/pinctrl/omap.h

and it is being used in am335x-evm.dts and am335x-boneblack.dts. Boneblack DTS uses PIN_OUTPUT_PULLUP and PIN_OUTPUT_PULLDOWN.

Thank you for reply Pavel,

I checked dts and dtsi files and it seems dt-bindings/pinctrl/am33xx.h gets included in our dts file however am335x.h includes omap.h So not sure who replaces what ? I assume defines in omap.h is overwritten by am335x.h

So if in my case when I used PIN_OUTPUT_PULLUP, it just selects PULLUP but won't make pin output ? and won't even enable PULLUP ? Or by default PIN state is output ? Because PIN_OUTPUT also just disables the PULLUP.

I went through the points you provided I think I understand however to make it clear I will write my understanding here.

So OUTPUT pull up helps in situation where after returning from Deep sleep we need pinstate to be high unless it is pulled low by driving pin low.

Is my understanding correct? Am I missing something ?

It depends on the specific pin you are using, as different pins has different default states. I would suggest you to check/read the pinmux registers value from user space with devmem2/omapconf tool, just you will be sure what is the final value.

Regards,
Pavel

Thank you for reply Pavel,

we have ZCE type AM3351.

I have following devicetree configuration

reset_eMMC: reset_eMMC {
		pinctrl-single,pins = <
			0x07C (PIN_OUTPUT_PULLUP | MUX_MODE7 )   /* gpmc_csn0.gpio1_29, BGA W8 (ZCE) RST_eMMC */
		>;
	};


	RESET_EMMC {
		pinctrl-names = "default";
		pinctrl-0 = <&reset_eMMC>;
		compatible = "gpio-leds";

		remmc {
			label = "reset_eMMC";
			gpios = <&gpio1 29 GPIO_ACTIVE_HIGH>;
			default-state = "on";
		};
	};

When I read pinmux register I see following value

# devmem2 0x44e1007c
/dev/mem opened.
Memory mapped at address 0xb6f64000.
Value at address 0x44E1007C (0xb6f6407c): 0x0

Now I don't know why 4th bit is 0. For 4th bit TRM says "0: Pulldown selected".

I see pin being high from sysfs I don't know why pulldown is selected.

GPIO_DATAOUT register also reads following value

# devmem2 0x4804c13c
/dev/mem opened.
Memory mapped at address 0xb6f1c000.
Value at address 0x4804C13C (0xb6f1c13c): 0x20000000

Default state of the pin on reset is H i.e. High-impedance with an active pullup resistor.

Thanks,

Regards,

Ankur

Ankur,

Ankur Tank said:

reset_eMMC: reset_eMMC { pinctrl-single,pins = < 0x07C (PIN_OUTPUT_PULLUP | MUX_MODE7 ) /* gpmc_csn0.gpio1_29, BGA W8 (ZCE) RST_eMMC */ >; };

What is this? Where you have found such pinmux format?

In AM335x TI PSDK 4.02 (kernel 4.9.59) we have the below pinmux format used:

linux-4.9.59/arch/arm/boot/dts/am335x-evm.dts

&am33xx_pinmux {
    pinctrl-names = "default";
    pinctrl-0 = <&matrix_keypad_s0 &volume_keys_s0 &clkout2_pin>;

    matrix_keypad_s0: matrix_keypad_s0 {
        pinctrl-single,pins = <
            AM33XX_IOPAD(0x854, PIN_OUTPUT_PULLDOWN | MUX_MODE7)    /* gpmc_a5.gpio1_21 */
            .........

>;
    };

davinci_mdio_default: davinci_mdio_default {
        pinctrl-single,pins = <
            /* MDIO */
            AM33XX_IOPAD(0x948, PIN_INPUT_PULLUP | SLEWCTRL_FAST | MUX_MODE0)    /* mdio_data.mdio_data */
            AM33XX_IOPAD(0x94c, PIN_OUTPUT_PULLUP | MUX_MODE0)            /* mdio_clk.mdio_clk */
        >;
    };

Another example is AM335x StarterKit DTS file:

linux-4.9.59/arch/arm/boot/dts/am335x-evmsk.dts

wl12xx_gpio: pinmux_wl12xx_gpio {
        pinctrl-single,pins = <
            AM33XX_IOPAD(0x87c, PIN_OUTPUT_PULLUP | MUX_MODE7) /* gpmc_csn0.gpio1_29 */
        >;
    };

Regards,
Pavel

Pavel,

Device tree snippet I posted is from custom board which we have,

That pinmux node is under &am33xx_pinmux  node, and actual RESET_EMMC node is under /  (root) node.

I am trying to configuration eMMC reset line, To create that node, I was referring evm dts file.

That's where questions about OUTPUT_PULLUP arose.

Thanks,

Regards,

Ankur

Hi Pavel,

I changed reset eMMC pin configuration to following

    reset_eMMC: reset_eMMC {
        pinctrl-single,pins = <
            0x07C (PIN_OUTPUT | MUX_MODE7)   /* gpmc_csn0.gpio1_29, BGA W8 (ZCE) RST_eMMC */
        >;
    };

Previously I was reading wrong pinmux register,

# devmem2 0x44E1087C
/dev/mem opened.
Memory mapped at address 0xb6f83000.
Value at address 0x44E1087C (0xb6f8387c): 0xF

Now PINMUX register value matches with pinmux configuration.

I dumped PULLUP as we don't have deepsleep mode.

Do you suggest to keep PULLUP?

Thanks,

Regards,

Ankur

Ankur,

Ankur Tank said:

Do you suggest to keep PULLUP?

If you need internal pullup on that output pin, then I suggest to keep PULLUP.

Regards,
Pavel