SK-AM62B: Pin Control cannot set PIN with PULL_UP

Hi Sean,

SeanHC Lin said:

after replacing the k3-am625-sk.dtb on the EVB, I cannot light up the LED.

Can you clarify what the outcome should be?


For LEDs, you would want to use PIN_OUTPUT so the output buffer will be enabled. PIN_INPUT will disable the output buffer and no voltage will flow out of the pin. PULL_UP/PULL_DOWN refers to the internal resistor status.

If you are trying to set the LED to ON when the board boots, try changing the default-trigger property. Here is the documentation for common LEDs: https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/tree/Documentation/devicetree/bindings/leds/common.txt

The userspace can control the LEDs under /sys/class/leds/ path.

Best Regards,
Anshu

Hi Anshu,

Ultimately, my goal is to preset All PIN voltages using PINMUX. Not just LED.

The LED is controllable under the /sys/class/leds path, but it is controlled by a high-layer LED driver. I just wonder how to control all pins by the lower layer pinctrl-single (PINMUX) driver.

Before this, I utilized PIN C17 (gpio1_49) for a proof of concept. The voltages can be configured via the pinctrl-single driver if the user describes them in the device tree.

Despite configuring pin C17 as PIN_OUTPUT, as per your suggestion, the associated LED does not light up.

git diff

        usr_led_pins_default: usr-led-pins-default {
                pinctrl-single,pins = <
-                       AM62X_IOPAD(0x244, PIN_OUTPUT, 7) /* (C17/B15) MMC1_SDWP.GPIO1_49 */
+                       AM62X_IOPAD(0x244, PIN_OUTPUT_PULLUP, 7) /* (C17/B15) MMC1_SDWP.GPIO1_49 */
                >;
        };

Thanks,

Sean

Hi Sean,

Just to clarify, you are trying to control the GPIO pins voltage states and you are testing this using the on-board LEDs. Is my understanding correct?

I think a better way of testing he pins would be to measure the voltage using a multimeter or another tool (or even an external resistor + LED depending on the pin).

Please also be aware that GPIO pins need a reference. You can follow this thread for an example: https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1268671/sk-am62-using-the-gpios-in-the-40-pin-user-expansion-port/4804378

Best Regards,
Anshu

Hi Anshu,

Yes, I want to control the GPIO pins and set an internal pull-up on it.

Using the gpioset tool to control the LED is working fine, but I still cannot set the internal pull-up on the PIN.

root@am62xx:~# gpioset gpiochip2 49=1 # turn on

root@am62xx:~# gpioset gpiochip2 49=0 # turn off

root@am62xx:~# gpioset gpiochip2 49=1 # turn on

The device tree that I am using is:

--- a/arch/arm64/boot/dts/ti/k3-am62x-sk-common.dtsi
+++ b/arch/arm64/boot/dts/ti/k3-am62x-sk-common.dtsi
@@ -105,19 +105,6 @@ framebuffer: framebuffer@ff700000 {
                };
        };

-       leds {
-               compatible = "gpio-leds";
-               pinctrl-names = "default";
-               pinctrl-0 = <&usr_led_pins_default>;
-
-               led-0 {
-                       label = "am62-sk:green:heartbeat";
-                       gpios = <&main_gpio1 49 GPIO_ACTIVE_HIGH>;
-                       linux,default-trigger = "heartbeat";
-                       function = LED_FUNCTION_HEARTBEAT;
-                       default-state = "off";
-               };
-       };

        tlv320_mclk: clk-0 {
                #clock-cells = <0>;
@@ -225,7 +212,7 @@ AM62X_IOPAD(0x240, PIN_INPUT, 0) /* (D17/C15) MMC1_SDCD */

        usr_led_pins_default: usr-led-pins-default {
                pinctrl-single,pins = <
-                       AM62X_IOPAD(0x244, PIN_OUTPUT, 7) /* (C17/B15) MMC1_SDWP.GPIO1_49 */
+                       AM62X_IOPAD(0x244, PIN_OUTPUT_PULLUP, 7) /* (C17/B15) MMC1_SDWP.GPIO1_49 */
                >;
        };

@@ -568,3 +555,9 @@ dpi1_out: endpoint {
                };
        };
 };
+
+&main_gpio1 {
+       pinctrl-names = "default";
+       pinctrl-0 = <&usr_led_pins_default>;
+       status = "okay";
+};

I believe the PIN is capable of internal pull-up, as the documentation states:

Is there anything else wrong?

Note: Using a multimeter to measure the voltage of the pin is the same as looking at the light from the LED.

Thanks,

Sean

Hi Sean,

I do not see any issues with the device tree you provided.

I looked further into this issue. You are correct that GPIO1_49 can have the pull-up or pull-down modifier, but looking into the schematic of the board, GPIO1_49 is connected to that LED which may explain why the pull resistor does not have an effect. You can find more information on pages 8 & 38 of the SK-AM62B schematics here: https://www.ti.com/tool/SK-AM62B#design-files.

Best Regards,
Anshu