Re: [PATCH] serial/8250: Set fifo timeout with uart_fifo_timeout()

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

On Sat, Nov 25, 2023 at 06:36:32AM +0000, Michael Pratt wrote:
> Commit 8f3631f0f6eb ("serial/8250: Use fifo in 8250 console driver")
> reworked functions for basic 8250 and 16550 type serial devices
> in order to enable and use the internal FIFO device for buffering,
> however the default timeout of 10 ms remained, which is proving
> to be insufficient for low baud rates like 9600, causing data overrun.
> 
> Unforunately, that commit was written and accepted just before commit
> 31f6bd7fad3b ("serial: Store character timing information to uart_port")
> which introduced the frame_time member of the uart_port struct
> in order to store the amount of time it takes to send one UART frame
> relative to the baud rate and other serial port configuration,
> and commit f9008285bb69 ("serial: Drop timeout from uart_port")
> which established function uart_fifo_timeout() in order to
> calculate a reasonable timeout to wait for all frames
> in the FIFO device to flush before writing data again
> using the now stored frame_time value and size of the buffer.
> 
> Fix this by using the new function to calculate the timeout
> whenever the buffer is larger than 1 byte (unknown port default).
> 
> Tested on a MIPS device (ar934x) at baud rates 625, 9600, 115200.

Do we need a Fixed tag?

...

>  	unsigned int status, tmout = 10000;
>  
> -	/* Wait up to 10ms for the character(s) to be sent. */
> +	/* Wait for a time relative to buffer size and baud */
> +	if (up->port.fifosize > 1)
> +		tmout = jiffies_to_usecs(uart_fifo_timeout(&up->port));

Why can't we simply use this one?

	unsigned int status, tmout;

	tmout = jiffies_to_usecs(uart_fifo_timeout(&up->port));
	for (;;) {

>  	for (;;) {
>  		status = serial_lsr_in(up);

-- 
With Best Regards,
Andy Shevchenko