On Tue, 16 Apr 2024, Michael Pratt wrote:
> This is a partial revert of Commit f9008285bb69
> ("serial: Drop timeout from uart_port").
>
> In order to prevent having to calculate a timeout
> for the fifo device during a write operation, if enabled,
> calculate it ahead of time and store the value of the timeout
> in a struct member of uart_port.
Hi,
Why is calculating during write bad/wrong, you don't give any real
justification for this change? You're talking about "low rates" in cover
letter, which makes it even more confusing because writes occur very
infrequently so a few math operations are nothing to be concerned of (in
timescales UARTs operate in, no math penalty is really worth even
discussing IMO).
--
i.
> Signed-off-by: Michael Pratt <mcpratt@xxxxx>
> ---
> V1 -> V2: new commit
>
> drivers/tty/serial/serial_core.c | 3 +++
> include/linux/serial_core.h | 1 +
> 2 files changed, 4 insertions(+)
>
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index ff85ebd3a007..9b3176d684a4 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -414,6 +414,9 @@ uart_update_timeout(struct uart_port *port, unsigned int cflag,
>
> temp *= NSEC_PER_SEC;
> port->frame_time = (unsigned int)DIV64_U64_ROUND_UP(temp, baud);
> +
> + if (port->fifosize > 1)
> + port->timeout = uart_fifo_timeout(port);
> }
> EXPORT_SYMBOL(uart_update_timeout);
>
> diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
> index 0a0f6e21d40e..c6422021152f 100644
> --- a/include/linux/serial_core.h
> +++ b/include/linux/serial_core.h
> @@ -561,6 +561,7 @@ struct uart_port {
>
> bool hw_stopped; /* sw-assisted CTS flow state */
> unsigned int mctrl; /* current modem ctrl settings */
> + unsigned long timeout; /* character-based timeout */
> unsigned int frame_time; /* frame timing in ns */
> unsigned int type; /* port type */
> const struct uart_ops *ops;
>
