Just saving off a hack today because this continues to be harder than it has to be based on topics like:
Below is just another hack and not the way we should solve this problem. Someone was bugging me for this and I honestly don’t a lot of the fuss, because I hack on device-tree at least a little bit every week. I know I shouldn’t expect other people to just know this stuff.
Anyway, I didn’t find a suitable overlay in the repository super-quickly and it is easier just to hack the base tree than to debug syntax on an overlay. So, the below yuck ensude…
jkridner@slotcar:~$ ssh debian@192.168.7.2
...
debian@BeaglePlay:~$ cd /opt/source/dtb-5.10-ti/
debian@BeaglePlay:/opt/source/dtb-5.10-ti$ wget https://paste.debian.net/download/1310703
...
debian@BeaglePlay:/opt/source/dtb-5.10-ti$ git apply 1310703
debian@BeaglePlay:/opt/source/dtb-5.10-ti$ make
DTC src/arm64/k3-am625-beagleplay.dtb
debian@BeaglePlay:/opt/source/dtb-5.10-ti$ sudo make install
...
debian@BeaglePlay:/opt/source/dtb-5.10-ti$ sudo shutdown -r now
Connection to 192.168.7.2 closed by remote host.
Connection to 192.168.7.2 closed.
jkridner@slotcar:~$ ssh debian@192.168.7.2
...
debian@BeaglePlay:~$ ls -l /dev/play/mikrobus/uart
lrwxrwxrwx 1 root root 11 Jun 18 2023 /dev/play/mikrobus/uart -> ../../ttyS3
debian@BeaglePlay:~$ gpioinfo | grep MB_
line 7: "MB_CIPO" unused output active-high
line 8: "MB_COPI" unused output active-high
line 9: "MB_INT" unused input active-high
line 10: "MB_AN" unused output active-high
line 11: "MB_PWM" unused output active-high
line 12: "MB_RST" unused output active-high
line 13: "MMB_CS" unused output active-high
line 14: "MB_SCK" unused output active-high
line 22: "MB_SCL" unused output active-high
line 23: "MB_SDA" unused output active-high
line 24: "MB_RX" unused output active-high
line 25: "MB_TX" unused output active-high
And, for reference, this was the device-tree hack:
diff --git a/src/arm64/k3-am625-beagleplay.dts b/src/arm64/k3-am625-beagleplay.dts
index b36764a..903ee33 100644
--- a/src/arm64/k3-am625-beagleplay.dts
+++ b/src/arm64/k3-am625-beagleplay.dts
@@ -286,7 +286,7 @@
pinctrl-names = "default", "pwm_default", "pwm_gpio",
"uart_default", "uart_gpio", "i2c_default",
"i2c_gpio", "spi_default", "spi_gpio";
- pinctrl-0 = <&mikrobus_gpio_pins_default>;
+ pinctrl-0 = <&mikrobus_uart_pins_default>;
pinctrl-1 = <&mikrobus_pwm_pins_default>;
pinctrl-2 = <&mikrobus_pwm_pins_gpio>;
pinctrl-3 = <&mikrobus_uart_pins_default>;
@@ -574,6 +574,14 @@
pinctrl-single,pins = <
AM62X_IOPAD(0x01d8, PIN_INPUT, 1) /* (C15) MCAN0_TX.UART5_RXD */
AM62X_IOPAD(0x01dc, PIN_OUTPUT, 1) /* (E15) MCAN0_RX.UART5_TXD */
+ AM62X_IOPAD(0x019c, PIN_INPUT, 7) /* (B18) MCASP0_AXR1.GPIO1_9 */
+ AM62X_IOPAD(0x01a0, PIN_INPUT, 7) /* (E18) MCASP0_AXR0.GPIO1_10 */
+ AM62X_IOPAD(0x01a4, PIN_INPUT, 7) /* (B20) MCASP0_ACLKX.GPIO1_11 */
+ AM62X_IOPAD(0x01a8, PIN_INPUT, 7) /* (D20) MCASP0_AFSX.GPIO1_12 */
+ AM62X_IOPAD(0x01d0, PIN_INPUT, 7) /* (A15) UART0_CTSn.GPIO1_22 */
+ AM62X_IOPAD(0x01d8, PIN_INPUT, 7) /* (C15) MCAN0_TX.GPIO1_24 */
+ AM62X_IOPAD(0x01dc, PIN_INPUT, 7) /* (E15) MCAN0_RX.GPIO1_25 */
+ AM62X_IOPAD(0x01d4, PIN_INPUT, 7) /* (B15) UART0_RTSn.GPIO1_23 */
>;
};
@@ -880,14 +888,14 @@
&main_gpio1 {
gpio-line-names = "", "", "", "", "", /* 0-4 */
- "SPE_RSTN", "SPE_INTN", "MIKROBUS_GPIO1_7", /* 5-7 */
- "MIKROBUS_GPIO1_8", "MIKROBUS_GPIO1_9", /* 8-9 */
- "MIKROBUS_GPIO1_10", "MIKROBUS_GPIO1_11", /* 10-11 */
- "MIKROBUS_GPIO1_12", "MIKROBUS_W1_GPIO0", /* 12-13 */
- "MIKROBUS_GPIO1_14", /* 14 */
+ "SPE_RSTN", "SPE_INTN", "MB_CIPO", /* 5-7 */
+ "MB_COPI", "MB_INT", /* 8-9 */
+ "MB_AN", "MB_PWM", /* 10-11 */
+ "MB_RST", "MMB_CS", /* 12-13 */
+ "MB_SCK", /* 14 */
"", "", "", "", "VDD_3V3_SD", "", "", /* 15-21 */
- "MIKROBUS_GPIO1_22", "MIKROBUS_GPIO1_23", /* 22-23 */
- "MIKROBUS_GPIO1_24", "MIKROBUS_GPIO1_25", /* 24-25 */
+ "MB_SCL", "MB_SDA", /* 22-23 */
+ "MB_RX", "MB_TX", /* 24-25 */
"", "", "", "", "", "", "", "", "", "", "", "", /* 26-37 */
"", "", "", "", "", "", "", "", "", "", /* 38-47 */
"SD_CD", "SD_VOLT_SEL", "", "", "", "", "", "", /* 48-55 */
@@ -1194,8 +1202,9 @@
};
&main_uart5 {
+ symlink = "play/mikrobus/uart";
status = "okay";
- force-empty-serdev-controller;
+ //force-empty-serdev-controller;
};
&main_uart6 {
This pointed out several problems to me and I feel like we need to attack this problem from multiple angles.
-
We need to document dynamic pinmuxing. There are a number of states that the mikrobus driver is smart enough to use within the kernel, but I have no idea how to make use of that stuff from user-space. It is very much worth taking some time to put a tutorial together specifically on this low-pin-count, very-normalized interface.
-
We need to enable and document dynamic device-tree overlays and find some way that upstream will take it. If we can disable these drivers from user-space, then it becomes a lot easier to explain how to do some user-space hacking to build some understanding before committing things to the booted device-tree or kernel code.
-
The device-tree needs a big overhaul clean-up. The names where not useful for the GPIO pins. I mean “MIKROBUS_GPIO1_11”? Which header pin is that on? If you have to go back to the schematic, we are missing the point of what Linux has to offer. We have this nice silkscreen on the board with names for every pin. Now, should I have renamed “MIRKOBUS_” to “MB_”? I don’t know. Just seems like a lot of letters that may or may not answer the question users are asking themselves.
-
We need to push all these update upstream.
-
We need to tie the solution into a tool like
bb-configwhich both provides an easy mechanism as well as codifies the approach we use as reference. I applaud new efforts likebeagle-kversion… I found that tool very helpful to get back to the default 5.10 kernel from the mainline kernel I was running on this board, but looking around for several tools feels like a real pain. We need a single front-end that acts as documentation for how to use what should be in the upstream kernel+device-tree+udev-customizations.
