logging: uart: support multiple instances

[ycsin]

Extends the UART log backend to support multiple UART instances.

Building samples/hello_world with qemu_x86 using additional Kconfigs:

CONFIG_LOG=y
CONFIG_LOG_BACKEND_UART=y

ROM reports:

main branch

Path                              Size
=======================================
log_backend_uart.c (ROM)           208
├── char_out                        49
├── dropped                         16
├── format_set                      15
├── log_backend_uart                16
├── log_backend_uart_api            28
├── log_backend_uart_init            1
├── log_const_log_uart               8
├── log_output_uart                 16
├── panic                           23
└── process                         36
=======================================
log_backend_uart.c (RAM)            26
├── backend_cb_log_backend_uart      8
├── in_panic                         1
├── log_format_current               4
├── log_output_uart_control_block   12
└── uart_output_buf                  1

This PR, using zephyr,console

Path                              Size
=======================================
log_backend_uart.c (ROM)           280
├── backend_cb_log_backend_uart0     8
├── char_out                        51
├── dropped                         22
├── format_set                      24
├── lbu_cb_ctx_0                    12
├── lbu_output_0                    16
├── log_backend_uart0               16
├── log_backend_uart_api            28
├── log_backend_uart_init           21
├── log_const_log_uart               8
├── panic                           29
└── process                         45
=======================================
log_backend_uart.c (RAM)            53
├── backend_cb_log_backend_uart0     8
├── lbu_buffer_0                     1
├── lbu_data_0                      32
└── lbu_output_0_control_block      12

	main	PR
RAM	122912	122912
ROM	56856	56864	+8
char_out	49	51	+2
dropped	16	22	+6
format_set	15	24	+9
log_backend_uart	16	16
log_backend_uart_api	28	28
log_backend_uart_init	1	21	+20
log_const_log_uart	8	8
log_output_uart	16	16
panic	23	29	+6
process	36	45	+9

This PR, using zephyr,log-uart, 2 instances

Path                              Size
=======================================
log_backend_uart.c                 332
├── backend_cb_log_backend_uart0     8
├── backend_cb_log_backend_uart1     8
├── char_out                        51
├── dropped                         22
├── format_set                      24
├── lbu_cb_ctx_0                    12
├── lbu_cb_ctx_1                    12
├── lbu_output_0                    16
├── lbu_output_1                    16
├── log_backend_uart0               16
├── log_backend_uart1               16
├── log_backend_uart_api            28
├── log_backend_uart_init           21
├── log_const_log_uart               8
├── panic                           29
└── process                         45
=======================================
log_backend_uart.c (RAM)           106
├── backend_cb_log_backend_uart0     8
├── backend_cb_log_backend_uart1     8
├── lbu_buffer_0                     1
├── lbu_buffer_1                     1
├── lbu_data_0                      32
├── lbu_data_1                      32
├── lbu_output_0_control_block      12
└── lbu_output_1_control_block      12

[cfriedt]

Would be also good to add the chosen to docs

https://docs.zephyrproject.org/latest/build/dts/api/api.html#zephyr-specific-chosen-nodes

[ycsin]

#65001

[cfriedt]

I think my preference would be either to use phandles property in the chosen node, or to simply use a child DT node under each UART selected to be a log backend.

However, the phandles approach does not seem to work for in the chosen node.

Personally, I think the chosen + node + phandles is kind of overkill.

[cfriedt]

Alternatively, if it were possible to support a phandle array in chosen, that would be kind of ideal, but it might require some additional devicetree hacks.

[nordicjm]

Can you do a build without these changes and with these changes (ARM cortex ideally) with 1 device and note the flash/RAM usage on both?

[nordic-krch]

+1 to @nordicjm suggestion. I guess there will be increase so it would be good to wrap instance getting in some macro so that there is no code addition when 1 uart is used (99.99% of cases).

[ycsin]

@nordic-krch @nordicjm

Building samples/hello_world with qemu_x86 using additional Kconfigs:

CONFIG_LOG=y
CONFIG_LOG_BACKEND_UART=y

ROM reports:

main branch

Path                              Size
=======================================
log_backend_uart.c (ROM)           208
├── char_out                        49
├── dropped                         16
├── format_set                      15
├── log_backend_uart                16
├── log_backend_uart_api            28
├── log_backend_uart_init            1
├── log_const_log_uart               8
├── log_output_uart                 16
├── panic                           23
└── process                         36
=======================================
log_backend_uart.c (RAM)            26
├── backend_cb_log_backend_uart      8
├── in_panic                         1
├── log_format_current               4
├── log_output_uart_control_block   12
└── uart_output_buf                  1

This PR, using zephyr,console

Path                              Size
=======================================
log_backend_uart.c (ROM)           280
├── backend_cb_log_backend_uart0     8
├── char_out                        51
├── dropped                         22
├── format_set                      24
├── lbu_cb_ctx_0                    12
├── lbu_output_0                    16
├── log_backend_uart0               16
├── log_backend_uart_api            28
├── log_backend_uart_init           21
├── log_const_log_uart               8
├── panic                           29
└── process                         45
=======================================
log_backend_uart.c (RAM)            53
├── backend_cb_log_backend_uart0     8
├── lbu_buffer_0                     1
├── lbu_data_0                      32
└── lbu_output_0_control_block      12

	main	PR
RAM	122912	122912
ROM	56856	56864	+8
char_out	49	51	+2
dropped	16	22	+6
format_set	15	24	+9
log_backend_uart	16	16
log_backend_uart_api	28	28
log_backend_uart_init	1	21	+20
log_const_log_uart	8	8
log_output_uart	16	16
panic	23	29	+6
process	36	45	+9

This PR, using zephyr,log-uart, 2 instances

Path                              Size
=======================================
log_backend_uart.c                 332
├── backend_cb_log_backend_uart0     8
├── backend_cb_log_backend_uart1     8
├── char_out                        51
├── dropped                         22
├── format_set                      24
├── lbu_cb_ctx_0                    12
├── lbu_cb_ctx_1                    12
├── lbu_output_0                    16
├── lbu_output_1                    16
├── log_backend_uart0               16
├── log_backend_uart1               16
├── log_backend_uart_api            28
├── log_backend_uart_init           21
├── log_const_log_uart               8
├── panic                           29
└── process                         45
=======================================
log_backend_uart.c (RAM)           106
├── backend_cb_log_backend_uart0     8
├── backend_cb_log_backend_uart1     8
├── lbu_buffer_0                     1
├── lbu_buffer_1                     1
├── lbu_data_0                      32
├── lbu_data_1                      32
├── lbu_output_0_control_block      12
└── lbu_output_1_control_block      12

[nordic-krch]

Checked that for cortex-m and riscv32 overhead is even smaller. Looks ok for me.