yangsong8-a1 opened a new pull request, #21746:
URL: https://github.com/apache/nuttx/pull/21746
## Summary
- Add a per-device recursive spinlock (`rspinlock_t lock`) to
`struct uart_dev_s`, plus `uart_spinlock()` / `uart_spinunlock()`.
The `nopreempt` argument also locks the scheduler while the lock is held.
- Use it instead of `enter_critical_section()` in the serial upper half,
the 16550 and CMSDK lower halves. The lock is released around
`nxsem_wait()`.
- 16550 `txint` holds the lock with the scheduler locked, so a wakeup inside
`uart_xmitchars()` cannot switch tasks while the lock is held.
- With `CONFIG_SERIAL_TXDMA`, take the lock around the `uart_dmatxavail()`
calls in `uart_readv()` and `uart_writev()`, which touch `dev->xmit`.
- pl011 `txint` uses the uart lock instead of the critical section, to keep
one lock order with `uart_xmitchars()`.
- A style-only commit fixes the existing nxstyle errors in serial_cmsdk.c.
## Impact
Serial drivers using `drivers/serial/serial.c`. One UART no longer takes the
global critical section, so it does not block other CPUs or drivers on SMP.
`struct uart_dev_s` grows by one `rspinlock_t`.
## Testing
Ubuntu 22.04, gcc 13.1, arm-none-eabi-gcc 10.3, aarch64-none-elf-gcc.
Builds (each commit on its own, no new warnings):
- Built and booted: sim:nsh, sim:smp, qemu-armv8a:nsh, qemu-armv8a:nsh_smp
(-smp 4, pl011), qemu-intel64:nsh (16550) with and without CONFIG_SMP
(-smp 4, KVM), mps2-an500:nsh (CMSDK).
- Built with `CONFIG_SERIAL_TXDMA=y`: sim:nsh, imxrt1180-evk:nsh,
nucleo-f446re:ihm08m1_f32.
Concurrent read/write stress test. A test app runs three threads on the
console at the same time:
- Writers A and B each write 1500 numbered lines (`WA 00000` ...
`WA 01499`, `WB ...`) to stdout. They sleep 10 ms every 5 lines so the two
interleave, call `FIONWRITE`/`FIONSPACE` every 100 lines and `tcdrain()`
every 500 lines. This exercises `uart_writev()`, `uart_putxmitbuf()`
(including the buffer-full wait), `uart_xmitchars()` from the TX
interrupt and `uart_tcdrain()`.
- A reader opens `/dev/console` with `O_NONBLOCK` and loops on
`poll(POLLIN, 10 ms)`, `read()` and `FIONREAD`. This exercises
`uart_poll()`, `uart_readv()` and `uart_recvchars()` from the RX
interrupt.
- While the test runs, the host types characters on the console (a line
every 200 ms), so RX interrupts, echo (and the `uart_dmatxavail()` echo
paths on sim, which uses TX DMA) run at the same time as the TX traffic.
- After the test, the host types another command to check that nsh still
responds.
Pass criteria: the console log contains exactly 1500 lines from each writer,
numbered 0..1499 in order with none lost or repeated, the app prints
`STRESS DONE`, and nsh responds afterwards (no deadlock or lost TX
wakeup).
```
sim:nsh A: 1500 lines, in order B: 1500 lines, in order PASS
qemu-armv8a:nsh_smp A: 1500 lines, in order B: 1500 lines, in order PASS
qemu-intel64 SMP x4 A: 1500 lines, in order B: 1500 lines, in order PASS
STRESS DONE rx=64 polls=16
```
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