Summary:
- I thought this cs is needed to avoid data corruption
- For example, while executing uart_xmitchar() in the interrupt
handler on CPU0, an application running on CPU1 can call
uart_putxmitchar() via write()->uart_write().
- In this case, taking xmit.sem in uart_write() will wait for CPU0
to finish uart_xmitchar() because CPU0 has already taken a cs
in uart_xmitchar() then nxsem_wait() on CPU0 takes a new cs
inside (and release the cs when returning but it's OK)
- Then uart_write() on CPU1 disables UART TX, so uart_xmitchar()
on CPU0 will not be called while executing uart_write() on CPU1.
- So this critical section in uart_putxmitchar() can be removed.
Impact:
- None
Testing:
- Tested with spresense:wifi_smp, esp32-devkitc:smp
Reported-by: Xiang Xiao <xiaoxiang@xiaomi.com>
Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>
3ccef09b4e