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serial: Store character timing information to uart_port

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Struct uart_port currently stores FIFO timeout. Having character timing
information readily available is useful. Even serial core itself
determines char_time from port->timeout using inverse calculation.

Store frame_time directly into uart_port. Character time is stored in
nanoseconds to have reasonable precision with high rates. To avoid
overflow, 64-bit math is necessary.

It might be possible to determine timeout from frame_time by
multiplying it with fifosize as needed but only part of the users seem
to be protected by a lock. Thus, this patch does not pursue storing
only frame_time in uart_port.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20220425143410.12703-2-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ilpo Järvinen 2022-04-25 17:33:58 +03:00 • committed by Greg Kroah-Hartman
parent 070e246217
commit 31f6bd7fad
2 changed files with 9 additions and 6 deletions
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14
drivers/tty/serial/serial_core.c
View file

@ -24,6 +24,7 @@
#include <linux/sysrq.h>
#include <linux/delay.h>
#include <linux/mutex.h>
#include <linux/math64.h>
#include <linux/security.h>
#include <linux/irq.h>
@ -338,15 +339,18 @@ void
uart_update_timeout(struct uart_port *port, unsigned int cflag,
unsigned int baud)
{
unsigned int size;
unsigned int size = tty_get_frame_size(cflag);
u64 frame_time;
size = tty_get_frame_size(cflag) * port->fifosize;
frame_time = (u64)size * NSEC_PER_SEC;
size *= port->fifosize;
/*
* Figure the timeout to send the above number of bits.
* Add .02 seconds of slop
*/
port->timeout = (HZ * size) / baud + HZ/50;
port->frame_time = DIV64_U64_ROUND_UP(frame_time, baud);
}
EXPORT_SYMBOL(uart_update_timeout);
@ -1643,10 +1647,8 @@ static void uart_wait_until_sent(struct tty_struct *tty, int timeout)
* Note: we have to use pretty tight timings here to satisfy
* the NIST-PCTS.
*/
char_time = (port->timeout - HZ/50) / port->fifosize;
char_time = char_time / 5;
if (char_time == 0)
char_time = 1;
char_time = max(nsecs_to_jiffies(port->frame_time / 5), 1UL);
if (timeout && timeout < char_time)
char_time = timeout;

1
include/linux/serial_core.h
View file

@ -232,6 +232,7 @@ struct uart_port {
int hw_stopped; /* sw-assisted CTS flow state */
unsigned int mctrl; /* current modem ctrl settings */
unsigned int timeout; /* character-based timeout */
unsigned int frame_time; /* frame timing in ns */
unsigned int type; /* port type */
const struct uart_ops *ops;
unsigned int custom_divisor;