On Fri, Oct 25, 2024 at 01:03:23PM +0206, John Ogness wrote:
> After a console has fed a line into TX, it uses wait_for_xmitr()
> to wait until the data has been sent out before returning to the
> printk code. However, wait_for_xmitr() will timeout after 10ms,
printk here is a function reference or module?
For the latter I would use the filename to be sure it's clear,
like printk.c. For the former (and it seems you know that)
we may use printk().
> regardless if the data has been transmitted or not.
>
> For single bytes, this timeout is sufficient even at very slow
> baud rates, such as 1200bps. However, when FIFO mode is used,
> there may be 64 bytes pushed into the FIFO at once. At a baud
> rate of 115200bps, the 10ms timeout is still sufficient.
> However, when using lower baud rates (such as 57600bps), the
> timeout is _not_ sufficient. This causes longer lines to be cut
> off, resulting in lost and horribly misformatted output on the
> console.
>
> When using FIFO mode, take the number of bytes into account to
> determine an appropriate max timeout. Increasing the timeout
maximum
(in order not to mix with max() function)
> does not affect performance since ideally the timeout never
> occurs.
...
> /*
> * Wait for transmitter & holding register to empty
> + * with timeout
Can you fix the style while at it?
> */
/* Wait for transmitter & holding register to empty with timeout */
...
> static void serial8250_console_fifo_write(struct uart_8250_port *up,
> const char *s, unsigned int count)
> {
> - int i;
> const char *end = s + count;
> unsigned int fifosize = up->tx_loadsz;
> + unsigned int tx_count = 0;
> bool cr_sent = false;
> + unsigned int i;
>
> while (s != end) {
> - wait_for_lsr(up, UART_LSR_THRE);
> + /* Allow timeout for each byte of a possibly full FIFO. */
Does the one-line comment style in this file use periods? If not, drop,
otherwise apply it to the above proposal.
> + for (i = 0; i < fifosize; i++) {
> + if (wait_for_lsr(up, UART_LSR_THRE))
> + break;
> + }
> + }
> +
> + /* Allow timeout for each byte written. */
> + for (i = 0; i < tx_count; i++) {
> + if (wait_for_lsr(up, UART_LSR_THRE))
> + break;
This effectively repeats the above. Even for the fix case I would still add
a new helper to deduplicate.
> }
> }
--
With Best Regards,
Andy Shevchenko
