Linux/AM3352: GPIO configuration in device tree

Ankur Tank

Expert 2985 points

Part Number: AM3352

Tool/software: Linux

We are beaglebone black based custom board with 256MB RAM and 512MB DDR.

We are using Linux kernel 3.12.

I was trying to configure three gpios as input in devicetree.

I want to achieve two things.

1. Configure(mux) GPIOs as input with PULLUP from devicetree

2. Get sysfs files for those GPIOs in sysfs so no need to export GPIOs but directly read the values.

Below devicetree snnipet I have used to configure pinmux,

am33xx_pinmux: pinmux@44e10800 {
		pinctrl-names = "default";

---------------cut-----------------------------


        product_id_pins: product_id_pins{
            pinctrl-single,pins = <
                    0x028 (PIN_INPUT_PULLUP | MUX_MODE7)  /* gpmc_ad10.gpio0_26, (ZCE) */
                    0x034 (PIN_INPUT_PULLUP | MUX_MODE7)  /* gpmc_ad13.gpio1_13, (ZCE) */
                    0x024 (PIN_INPUT_PULLUP | MUX_MODE7)  /* gpmc_ad12.gpio1_12, (ZCE), */
            >;
        };
};


pid {

            pinctrl-names = "default";
            pinctrl-0 = <&product_id_pins>;
};

With this I need to write following shell command to read those GPIOs

# echo 26 > /sys/class/gpio/export
# echo 44 > /sys/class/gpio/export
# echo 45 > /sys/class/gpio/export

# cat /sys/class/gpio/gpio26/value 
0

# cat /sys//class/gpio/gpio44/value 
0

# cat /sys//class/gpio/gpio45/value 
0

Now nothing is connected on these GPIO pins, so value must be read high but values are low.

other sysfs entries read following

# grep -r . /sys/class/gpio/gpio26/
/sys/class/gpio/gpio26/edge:none
/sys/class/gpio/gpio26/power/control:auto
/sys/class/gpio/gpio26/power/runtime_active_time:0
/sys/class/gpio/gpio26/power/runtime_status:unsupported
/sys/class/gpio/gpio26/power/runtime_suspended_time:0
/sys/class/gpio/gpio26/value:0
/sys/class/gpio/gpio26/active_low:0
/sys/class/gpio/gpio26/direction:in

# grep -r . /sys/class/gpio/gpio44/
/sys/class/gpio/gpio44/edge:none
/sys/class/gpio/gpio44/power/control:auto
/sys/class/gpio/gpio44/power/runtime_active_time:0
/sys/class/gpio/gpio44/power/runtime_status:unsupported
/sys/class/gpio/gpio44/power/runtime_suspended_time:0
/sys/class/gpio/gpio44/value:0
/sys/class/gpio/gpio44/active_low:0
/sys/class/gpio/gpio44/direction:in

# grep -r . /sys/class/gpio/gpio45/
/sys/class/gpio/gpio45/edge:none
/sys/class/gpio/gpio45/power/control:auto
/sys/class/gpio/gpio45/power/runtime_active_time:0
/sys/class/gpio/gpio45/power/runtime_status:unsupported
/sys/class/gpio/gpio45/power/runtime_suspended_time:0
/sys/class/gpio/gpio45/value:0
/sys/class/gpio/gpio45/active_low:0
/sys/class/gpio/gpio45/direction:in

It has something to do with devicetree configuration.

Can someone suggest which client device I should configure in devicetree for those GPIOs ?

Thank you,

Regards,

Ankur

over 7 years ago

0 Biser Gatchev-XID over 7 years ago

TI__Guru**** 393215 points

The software team have been notified. They will respond here.

0 Prabhakar Lad over 7 years ago

Guru 11260 points

Hello,

once you have configured the pinumx as input, It should be by default configured as input. what is the value of direction (# cat /sys/class/gpio/gpio26/direction), now if you apply some current do you see value changing to 1 ?

Cheers,
--Prabhakar Lad

0 Ankur Tank over 7 years ago in reply to Prabhakar Lad

Expert 2985 points

Thank you for reply Prabhakar,
I have copied all the sysfs parameter above,

/sys/class/gpio/gpio26/direction reads "in"

Moreover I read the 0x44e10828(gpmc_ad10-gpio0_26) register's value using omapconf , it reads ox27 (receiver enabled and mode 7) But what I need is ox37( receiver enabled, input and mode7).

So it is configured as input but I also need the input pullup to be enabled which is not getting enabled.

If I do pinmuxing from u-boot that works but with the current stage of development we won't be able to update bootloader in the field.

Thank you,

Regards,
Ankur

0 Ankur Tank over 7 years ago in reply to Ankur Tank

Expert 2985 points

With some modification I am able to get pinmux right.

am33xx_pinmux: pinmux@44e10800 {
	pinctrl-names = "default";

----------------CUT---------------

        product_id_pins: product_id_pins{
            pinctrl-single,pins = <
                    0x028 (INPUT_EN | PULL_UP | MUX_MODE7 )  /* gpmc_ad10.gpio0_26, BGA T12 (ZCE) */
                    0x034 (INPUT_EN | PULL_UP | MUX_MODE7 )  /* gpmc_ad13.gpio1_13, BGA T13 (ZCE) */
                    0x030 (INPUT_EN | PULL_UP | MUX_MODE7 )  /* gpmc_ad12.gpio1_12, BGA U13 (ZCE), TP39 */
            >;
        };
};

pid {

            pinctrl-names = "default";
            pinctrl-0 = <&product_id_pins>;
			compatible = "gpio-leds";
};

With These changes I have to use following commands to read gpios,

echo 26 > /sys/class/gpio/export
echo 44 > /sys/class/gpio/export
echo 45 > /sys/class/gpio/export

cat /sys/class/gpio/gpio26/value
cat /sys/class/gpio/gpio44/value
cat /sys/class/gpio/gpio45/value

I have used compatible driver as "gpio-leds" which is not right.

And I wanted to create node for each gpio so that I can read gpio without exporting them.

Any suggestions ?

0 Cvetolin Shulev-XID over 7 years ago in reply to Ankur Tank

TI__Guru 65405 points

Hi Ankur,

Here are some useful resources about GPIO configuring and management:
processors.wiki.ti.com/index.php
processors.wiki.ti.com/.../Processor_SDK_Linux_GPIO_Driver_Overview
www.kernel.org/.../sysfs.txt

BR
Tsvetolin Shulev

0 Ankur Tank over 7 years ago in reply to Cvetolin Shulev-XID

Expert 2985 points

Hi Tsvetolin Shulev,

Thank you for reply,
I have referred the documents which you pointed me too,
From that I conclude that I can't create custom nodes for gpio like /sys/class/gpio/pid1 (controlling gpio26), /sys/class/gpio/pid2(controlling gpio44) etc .
I have to export gpio by its number and use it as i have mentioned above.
Is my understanding correct ?

Thank you,

Regards,
Ankur

0 Cvetolin Shulev-XID over 7 years ago in reply to Ankur Tank

TI__Guru 65405 points

Yes, your understanding is correct.

BR
Tsvetolin Shulev

0 Ankur Tank over 7 years ago in reply to Cvetolin Shulev-XID

Expert 2985 points

Can we not configure them as gpio-keys ?

I tried but running into

[ 0.423595] gpio-keys gpio_keys: Button without keycode: 0x1a
[ 0.423638] gpio-keys: probe of gpio_keys failed with error -22

Thank you,

Regards,
Ankur

Processors

Processors forum

Linux/AM3352: GPIO configuration in device tree