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

[Andy Shevchenko <andriy.shevchenko@intel.com>]

On Fri, Aug 28, 2026 at 02:45:17PM +0000, Tate Whiteberg wrote:
> If mid8250_set_termios is called while data is still in transmission,

mid8250_set_termios()

> 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 tag?

...

> static void mid8250_set_termios(struct uart_port *p, struct ktermios *termios,

>  {
>  	unsigned int baud = tty_termios_baud_rate(termios);
>  	struct mid8250 *mid = p->private_data;
> +	struct uart_8250_port *up = up_to_u8250p(p);

Move it one line up.

>  	unsigned short ps = 16;
>  	unsigned long fuart = baud * ps;
>  	unsigned long w = BIT(24) - 1;

>  	/* Gracefully handle the B0 case: fall back to B9600 */
>  	fuart = fuart ? fuart : 9600 * 16;
>  
> +	uart_port_lock_irq(p);

+ blank line.

Do we need to protect the preliminary calculations?

>  	if (mid->board->freq < fuart) {
>  		/* Find prescaler value that satisfies Fuart < Fref */
>  		if (mid->board->freq > baud)
> @@ -231,11 +233,14 @@ static void mid8250_set_termios(struct uart_port *p, struct ktermios *termios,
>  	}
>  
>  	rational_best_approximation(fuart, mid->board->freq, w, w, &mul, &div);

> +	serial8250_wait_for_xmitr(up, UART_LSR_BOTH_EMPTY);

Can't it be done one line after? Somewhere...

>  	p->uartclk = fuart * 16 / ps;		/* core uses ps = 16 always */

...here?

>  	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);

+ blank line.

> +	uart_port_unlock_irq(p);
>  
>  	serial8250_do_set_termios(p, termios, old);

...

> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index 38fa45e74a37..4eaf417f1fd7 100644

All below better to split to another prerequisite patch.

-- 
With Best Regards,
Andy Shevchenko