AM62x Enable UART2

Hi,

On the AM62x how do we enable UART2 during the Yocto build? We have created our own machine variation of k3-am62x-mitysom and created a dts file for it per the wiki instructions you provided. We thought we need to add this...

&main_uart2 {
    pinctrl-names = "default";
    pinctrl-0 = <&main_uart2_pins>;
    status = "okay";
};

main_uart2_pins: main-uart2-pins {
    pinctrl-single,pins = <
        AM62X_IOPAD(0x1d4, PIN_OUTPUT, 3) /* (B15) UART2_TXD Console */
        AM62X_IOPAD(0x1d0, PIN_INPUT, 3) /* (A15) UART2_RXD Console */
    >;
};

We also removed those pins from "main_gpio_p3_pins_default" since we muxed them.

It doesn't seem to be working when I cat /proc/tty/driver/serial.

I also see the below error at boot so it may be related.

[    1.509258] omap8250 2820000.serial: failed to get alias

Any help would be appreciated.

Tim

Replies (6)

RE: AM62x Enable UART2 - Added by Bob Duke 16 days ago

Tim,

What you have shown looks OK. Can you share your entire device tree file ? Nathan has access to our private project if you prefer to post the information there. You could also share your boot log and the output of cat /proc/tty/driver/serial.

Thanks,
-Bob

RE: AM62x Enable UART2 - Added by Jonathan Cormier 16 days ago

I'm not sure why but it seems like setting the serial alias is required.

8250_omap.c:


    ret = of_alias_get_id(np, "serial");
    if (ret < 0) {
        dev_err(&pdev->dev, "failed to get alias\n");
        return ret;
    }

There are currently several serial aliases set in the k3-am62x-mitysom-som.dtsi file, I'd recommend skipping a few numbers to prevent conflicts in the future if more serial aliases are added.

    aliases {
        serial0 = &mcu_uart0;
        serial1 = &wkup_uart0;
        serial2 = &main_uart0;
...

Example of adding the alias

diff --git a/arch/arm64/boot/dts/ti/k3-am62x-mitysom-devkit.dts b/arch/arm64/boot/dts/ti/k3-am62x-mitysom-devkit.dts
index 229f95f7c292..d900051e56c1 100644
--- a/arch/arm64/boot/dts/ti/k3-am62x-mitysom-devkit.dts
+++ b/arch/arm64/boot/dts/ti/k3-am62x-mitysom-devkit.dts
@@ -10,6 +10,10 @@
 #include "k3-am62x-mitysom-som.dtsi" 

 / {
+       aliases {
+               serial10 = &main_uart2;
+       };
+
        vcc_12v: vcc_12v {

Then the port will show up as ttyS10 since we set the alias to serial5

root@mitysom-am62x:~# dmesg | grep serial
[    1.476861] 2800000.serial: ttyS2 at MMIO 0x2800000 (irq = 238, base_baud = 3000000) is a 8250
[    1.507633] 2820000.serial: ttyS10 at MMIO 0x2820000 (irq = 240, base_baud = 3000000) is a 8250

RE: AM62x Enable UART2 - Added by Tim Troester 16 days ago

Bob,

Thanks for the response. I was getting ready to reply saying that I was able to get it working. Here is what I did in case it helps others.

Removed the previous mapping of the pins we wanted to use for UART2. There were being muxed as GPIO pins.
~~AM62X_IOPAD(0x01d0, PIN_INPUT_PULLDOWN, 7) /* (A15) UART0_CTSn.GPIO1_22 */~~
~~AM62X_IOPAD(0x01d4, PIN_INPUT_PULLDOWN, 7) /* (B15) UART0_RTSn.GPIO1_23 */~~

Muxed the pins to be part of UART2.

main_uart2_pins: main-uart2-pins {
    pinctrl-single,pins = <
        AM62X_IOPAD(0x1d4, PIN_OUTPUT, 3) /* (B15) UART2_TXD Console */
        AM62X_IOPAD(0x1d0, PIN_INPUT, 3) /* (A15) UART2_RXD Console */
    >;
};

Altered main_uart2 to use the pins that were repurposed and to enable it.

&main_uart2 {
    pinctrl-names = "default";
    pinctrl-0 = <&main_uart2_pins>;
    status = "okay";
};

Added an alias for uart2 (this is what I missing in my original question). This serial port will now be at /dev/ttyS4 (I would have used "serial2" but it was being used by something else).
```
&{/} {
    aliases {
      serial4 = &main_uart2;
    };
};
```