b_l072z_lrwan1 usart dma doesn't work

[M1cha]

Describe the bug
DMA doesn't seem to work with UART on this board.
It looks like data is neither received nor sent.

Please also mention any information which could help others to understand
the problem you're facing:

• b_l072z_lrwan1
• If you enable UART debugging, you can see that incoming data does generate interrupts, but the DMA buffer status doesn't show any change.
• I've tried both usart1 and usart2
• I don't understand the dmas config 100% and copied it from disco_l475_iot1.overlay, so I wouldn't exclude a user error.

To Reproduce
Steps to reproduce the behavior:

1. Apply patch
2. connect PA9 and PA10 to each other
3. west build -b b_l072z_lrwan1 zephyr/tests/drivers/uart/uart_async_api
4. west flash -r openocd
5. tests fail

Expected behavior
The tests should succeed. More specifically, the DMA should be able to send and receive data.

Impact
It prevents using the async UART API with this board.

Logs and console output

Running TESTSUITE uart_async_test
===================================================================
START - test_single_read_setup
 PASS - test_single_read_setup in 0.1 seconds
===================================================================
START - test_single_read
D: async rx enabled
D: tx: l=5
D: async timer started for 100000 us
D: tx abort: 0
D: tx: async timeout

    Assertion failed at WEST_TOPDIR/zephyr/tests/drivers/uart/uart_async_api/src/test_uart_async.c:87: test_single_read: (k_sem_take(&tx_done, K_MSEC(100)) not equal to 0)
TX_DONE timeout
 FAIL - test_single_read in 0.228 seconds

Environment (please complete the following information):

• OS: Linux
• Toolchain: Zephyr SDK
• Version: fa2054f93e4e80b079a4a6a9e84d642e51912042 (tag: v3.1.0-rc3)

Additional context

• A log from a different test setup where I simply did an infinite async read and sent data to the board. I added more logs to the driver to see what's going on with the DMA buffer. The idle interrupt happens when I send a character.

[00:00:05.620,000] <dbg> uart_stm32: uart_stm32_isr: idle interrupt occurred
[00:00:05.620,000] <dbg> uart_stm32: async_timer_start: async timer started for 3333 us
[00:00:05.623,000] <dbg> uart_stm32: uart_stm32_async_rx_timeout: rx timeout
[00:00:05.624,000] <dbg> uart_stm32: uart_stm32_dma_rx_flush: rx: flush
[00:00:05.624,000] <dbg> uart_stm32: uart_stm32_dma_rx_flush: rx: flush: buflen=64 pending=64 len: 0

• Patch file for adding support to b_l072z_lrwan1 to the test:

diff --git a/tests/drivers/uart/uart_async_api/boards/b_l072z_lrwan1.overlay b/tests/drivers/uart/uart_async_api/boards/b_l072z_lrwan1.overlay
new file mode 100644
index 0000000000..f0a25833cf
--- /dev/null
+++ b/tests/drivers/uart/uart_async_api/boards/b_l072z_lrwan1.overlay
@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: Apache-2.0 */
+
+&usart1 {
+       dmas = <&dma1 2 2 0x20440>,
+               <&dma1 3 2 0x20480>;
+       dma-names = "tx", "rx";
+};
+
+&dma1 {
+       status = "okay";
+};
diff --git a/tests/drivers/uart/uart_async_api/src/test_uart.h b/tests/drivers/uart/uart_async_api/src/test_uart.h
index b52176fe43..4d7f6398b1 100644
--- a/tests/drivers/uart/uart_async_api/src/test_uart.h
+++ b/tests/drivers/uart/uart_async_api/src/test_uart.h
@@ -67,6 +67,8 @@
 #elif defined(CONFIG_BOARD_MIMXRT1010_EVK) || \
        defined(CONFIG_BOARD_MIMXRT1015_EVK)
 #define UART_DEVICE_NAME DT_LABEL(DT_NODELABEL(lpuart4))
+#elif defined(CONFIG_BOARD_B_L072Z_LRWAN1)
+#define UART_DEVICE_NAME DT_LABEL(DT_NODELABEL(usart1))
 #else
 #define UART_DEVICE_NAME DT_LABEL(DT_CHOSEN(zephyr_console))
 #endif

[M1cha]

I've updated the patch to use DMA channels which actually support usart1. Unfortunately, that didn't help.

[M1cha]

Okay I managed to get it working by setting the dma slot to 3 like this:

       dmas = <&dma1 2 3 0x20440>,
                    <&dma1 3 3 0x20480>;

I found that by trial & error and have no idea where I'd find that information. I thought you're free to choose the slot when using a dmamux (which I'm not using).

[erwango]

Okay I managed to get it working by setting the dma slot to 3:

       dmas = <&dma1 2 2 0x20440>,
                    <&dma1 3 2 0x20480>;

I found that by trial & error and have no idea where I'd find that information. I thought you're free to choose the slot when using a dmamux (which I'm not using).

If I'm correct this information could be found in ref man (RM076.pdf), Table 51. Summary of the DMA requests for each channel

[M1cha]

well that's where I found the compatible channels(USART1_TX=2,4, USART2_RX=3,5) but I can't find what zephyr calls slot which is the fourth argument in the array(with &dma1 being the first)

[M1cha]

sry but the message you quoted from me still had the broken dts config, I updated it to what is currently working for me.

[erwango]

ok, this is described in https://docs.zephyrproject.org/latest/build/dts/api/bindings/dma/st%2Cstm32-dma-v2.html

[erwango]

@M1cha Can you confirm this answers your point ?