On Fri, Oct 25, 2024 at 04:45:02PM +0300, Andy Shevchenko wrote:
> 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.
>
> > }
> > }
Forgot to add, with the above being addressed, feel free to add
Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
--
With Best Regards,
Andy Shevchenko
