tty_port: drop last traces of low_latency

The main purpose of tty_port::low_latency was removed in commit
a9c3f68f3cd8 (tty: Fix low_latency BUG) back in 2014. It was left in
place for drivers as an optional tune knob. But only one driver has been
using it until the previous commit. So remove this misconcept
completely, given there are no users.

Signed-off-by: Jiri Slaby <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/networking/caif/caif.rst

···
 * tty_status: Prints the bit-mask tty status information
 
   - 0x01 - tty->warned is on.
-  - 0x02 - tty->low_latency is on.
   - 0x04 - tty->packed is on.
   - 0x08 - tty->flow_stopped is on.
   - 0x10 - tty->hw_stopped is on.

drivers/char/pcmcia/synclink_cs.c

···
 		printk("%s(%d):mgslpc_open(%s), old ref count = %d\n",
 			 __FILE__, __LINE__, tty->driver->name, port->count);
 
-	port->low_latency = (port->flags & ASYNC_LOW_LATENCY) ? 1 : 0;
-
 	spin_lock_irqsave(&info->netlock, flags);
 	if (info->netcount) {
 		retval = -EBUSY;

drivers/net/caif/caif_serial.c

···
 	ser->tty_status =
 		ser->tty->stopped << 5 |
 		ser->tty->flow_stopped << 3 |
-		ser->tty->packet << 2 |
-		ser->tty->port->low_latency << 1;
+		ser->tty->packet << 2;
 }
 static inline void debugfs_init(struct ser_device *ser, struct tty_struct *tty)
 {

drivers/s390/char/con3215.c

···
 
 	tty_port_tty_set(&raw->port, tty);
 
-	raw->port.low_latency = 0; /* don't use bottom half for pushing chars */
 	/*
 	 * Start up 3215 device
 	 */

drivers/s390/char/sclp_tty.c

···
 {
 	tty_port_tty_set(&sclp_port, tty);
 	tty->driver_data = NULL;
-	sclp_port.low_latency = 0;
 	return 0;
 }
 

drivers/s390/char/sclp_vt220.c

···
 {
 	if (tty->count == 1) {
 		tty_port_tty_set(&sclp_vt220_port, tty);
-		sclp_vt220_port.low_latency = 0;
 		if (!tty->winsize.ws_row && !tty->winsize.ws_col) {
 			tty->winsize.ws_row = 24;
 			tty->winsize.ws_col = 80;

drivers/s390/char/tty3270.c

···
 		tty->driver_data = tp;
 		tty->winsize.ws_row = tp->view.rows - 2;
 		tty->winsize.ws_col = tp->view.cols;
-		tp->port.low_latency = 0;
 		tp->inattr = TF_INPUT;
 		goto port_install;
 	}
···
 		return rc;
 	}
 
-	tp->port.low_latency = 0;
 	tty->winsize.ws_row = tp->view.rows - 2;
 	tty->winsize.ws_col = tp->view.cols;
 

drivers/tty/amiserial.c

···
 	state->custom_divisor = ss->custom_divisor;
 	port->close_delay = ss->close_delay * HZ/100;
 	port->closing_wait = ss->closing_wait * HZ/100;
-	port->low_latency = (port->flags & ASYNC_LOW_LATENCY) ? 1 : 0;
 
 check_and_exit:
 	if (tty_port_initialized(port)) {
···
 	port->tty = tty;
 	tty->driver_data = info;
 	tty->port = port;
-
-	port->low_latency = (port->flags & ASYNC_LOW_LATENCY) ? 1 : 0;
 
 	retval = startup(tty, info);
 	if (retval) {

drivers/tty/hvc/hvcs.c

···
 		hvcsd->todo_mask |= HVCS_QUICK_READ;
 
 	spin_unlock_irqrestore(&hvcsd->lock, flags);
-	/* This is synch because tty->low_latency == 1 */
+	/* This is synch -- FIXME :js: it is not! */
 	if(got)
 		tty_flip_buffer_push(&hvcsd->port);
 

drivers/tty/ipwireless/tty.c

···
 
 	tty->port.tty = linux_tty;
 	linux_tty->driver_data = tty;
-	tty->port.low_latency = 1;
 
 	if (tty->tty_type == TTYTYPE_MODEM)
 		ipwireless_ppp_open(tty->network);

drivers/tty/mxser.c

···
 				(ss->flags & ASYNC_FLAGS));
 		port->close_delay = ss->close_delay * HZ / 100;
 		port->closing_wait = ss->closing_wait * HZ / 100;
-		port->low_latency = (port->flags & ASYNC_LOW_LATENCY) ? 1 : 0;
 		if ((port->flags & ASYNC_SPD_MASK) == ASYNC_SPD_CUST &&
 				(ss->baud_base != info->baud_base ||
 				ss->custom_divisor !=

drivers/tty/serial/ifx6x60.c

···
 	/* put port data into this tty */
 	tty->driver_data = ifx_dev;
 
-	/* allows flip string push from int context */
-	port->low_latency = 1;
-
 	/* set flag to allows data transfer */
 	set_bit(IFX_SPI_STATE_IO_AVAILABLE, &ifx_dev->flags);
 

drivers/tty/serial/max3100.c

···
 			MAX3100_STATUS_PE | MAX3100_STATUS_FE |
 			MAX3100_STATUS_OE;
 
-	/* we are sending char from a workqueue so enable */
-	s->port.state->port.low_latency = 1;
-
 	if (s->poll_time > 0)
 		del_timer_sync(&s->timer);
 

drivers/tty/serial/serial_core.c

···
 	port->closing_wait    = closing_wait;
 	if (new_info->xmit_fifo_size)
 		uport->fifosize = new_info->xmit_fifo_size;
-	port->low_latency = (uport->flags & UPF_LOW_LATENCY) ? 1 : 0;
 
  check_and_exit:
 	retval = 0;
···
 	uport = uart_port_check(state);
 	if (!uport || uport->flags & UPF_DEAD)
 		return -ENXIO;
-
-	port->low_latency = (uport->flags & UPF_LOW_LATENCY) ? 1 : 0;
 
 	/*
 	 * Start up the serial port.

drivers/tty/synclink_gt.c

···
 	DBGINFO(("%s open, old ref count = %d\n", info->device_name, info->port.count));
 
 	mutex_lock(&info->port.mutex);
-	info->port.low_latency = (info->port.flags & ASYNC_LOW_LATENCY) ? 1 : 0;
 
 	spin_lock_irqsave(&info->netlock, flags);
 	if (info->netcount) {

include/linux/tty.h

···
 	wait_queue_head_t	delta_msr_wait;	/* Modem status change */
 	unsigned long		flags;		/* User TTY flags ASYNC_ */
 	unsigned long		iflags;		/* Internal flags TTY_PORT_ */
-	unsigned char		console:1,	/* port is a console */
-				low_latency:1;	/* optional: tune for latency */
+	unsigned char		console:1;	/* port is a console */
 	struct mutex		mutex;		/* Locking */
 	struct mutex		buf_mutex;	/* Buffer alloc lock */
 	unsigned char		*xmit_buf;	/* Optional buffer */