Re: [PATCH 1/3] serial: 8250_dw: Keep the BUSY-safe divisor hook when DLF is present

[sashiko-bot@kernel.org]

> dw8250_probe() installs dw8250_set_divisor(), which brackets the
> DLAB/DLL/DLH sequence with dw8250_idle_enter()/dw8250_idle_exit() so that
> a BUSY UART cannot drop the divisor LCR write. dw8250_setup_port() runs
> afterwards and replaces that hook with the dwlib one whenever it detects
> a DLF register. The dwlib hook programs the divisor through
> serial8250_do_set_divisor() without entering idle.
> 
> When termios changes while the UART is transmitting, the LCR|DLAB write
> is ignored and dw8250_check_lcr() retries it between
> dw8250_idle_enter() and dw8250_idle_exit(). dw8250_idle_exit() restores
> IER while DLAB is still set, so the value lands in DLH. The real IER
> keeps the zero written by dw8250_idle_enter(), and the port gets no
> further TX or RX interrupts while up->ier says they're enabled.
> 
> Program DLF from dw8250_set_divisor() inside the idle section and keep
> that hook after dw8250_setup_port().
> 
> Observed on an Allwinner A733 (Radxa Cubie A7Z): the first interactive
> tcsetattr() during console output left hardware IER at 0 and up->ier at
> 0x07. The shell never printed its prompt or read input. With this change
> alone the same boot reached the prompt and echoed input, and hardware
> IER matched up->ier afterwards.
> 
> Fixes: a7b9ce39fbe4 ("serial: 8250_dw: Ensure BUSY is deasserted")
> Cc: stable@vger.kernel.org
> Signed-off-by: Vinicius Pedrosa <vinicius.eduardo.pedrosa@gmail.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20261005172538.398522-1-vinicius.eduardo.pedrosa@gmail.com?part=1