Re: [PATCH v2 2/2] serial: 8250_mid: wait for LSR tx empty before setting termios

[Andy Shevchenko]

On Fri, Aug 28, 2026 at 05:57:28PM +0000, Tate Whiteberg wrote:
> If mid8250_set_termios() is called while data is still in transmission,
> the corresponding register updates will corrupt the transmission.
> 
> Fix this by locking the port and and waiting for the transmitter to
> empty before performing updates. It is necessary to wait for both
> UART_LSR_THRE and UART_LSR_TEMT to ensure the final character is sent.

> Fixes: d9eda9bab237 ("serial: 8250_pci: Intel MID UART support to its own driver")

Obviously this is not the commit when the problem appeared.
Check the commit f549e94effa1 ("serial: 8250_pci: add Intel Penwell ports").

...

> +	uart_port_lock_irq(p);
> +
>  	p->uartclk = fuart * 16 / ps;		/* core uses ps = 16 always */

+ blank line

> +	serial8250_wait_for_xmitr(up, UART_LSR_BOTH_EMPTY);
>  
>  	writel(ps, p->membase + INTEL_MID_UART_PS);		/* set PS */
>  	writel(mul, p->membase + INTEL_MID_UART_MUL);		/* set MUL */
>  	writel(div, p->membase + INTEL_MID_UART_DIV);
>  
> +	uart_port_unlock_irq(p);

-- 
With Best Regards,
Andy Shevchenko