Commit 31f6bd7f authored by Ilpo Järvinen's avatar Ilpo Järvinen Committed by Greg Kroah-Hartman
Browse files

serial: Store character timing information to uart_port 



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: default avatarIlpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20220425143410.12703-2-ilpo.jarvinen@linux.intel.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 070e2462

drivers/tty/serial/serial_core.c

+8 −6
Original line number Diff line number Diff line
@@ -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;

include/linux/serial_core.h

+1 −0
Original line number Diff line number Diff line
@@ -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;