tty_port: drop last traces of low_latency

The main purpose of tty_port::low_latency was removed in commit
a9c3f68f (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 <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20210105120239.28031-11-jslaby@suse.czSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/networking/caif/caif.rst

@@ -68,7 +68,6 @@ There are debugfs parameters provided for serial communication.
 * 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

@@ -2494,8 +2494,6 @@ static int mgslpc_open(struct tty_struct *tty, struct file * filp)
 		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

@@ -89,8 +89,7 @@ static inline void update_tty_status(struct ser_device *ser)
 	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

@@ -914,7 +914,6 @@ static int tty3215_open(struct tty_struct *tty, struct file * filp)
 
 	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

@@ -65,7 +65,6 @@ sclp_tty_open(struct tty_struct *tty, struct file *filp)
 {
 	tty_port_tty_set(&sclp_port, tty);
 	tty->driver_data = NULL;
-	sclp_port.low_latency = 0;
 	return 0;
 }
 

drivers/s390/char/sclp_vt220.c

@@ -560,7 +560,6 @@ sclp_vt220_open(struct tty_struct *tty, struct file *filp)
 {
 	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

@@ -967,7 +967,6 @@ static int tty3270_install(struct tty_driver *driver, struct tty_struct *tty)
 		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;
 	}
@@ -996,7 +995,6 @@ static int tty3270_install(struct tty_driver *driver, struct tty_struct *tty)
 		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

@@ -998,7 +998,6 @@ static int set_serial_info(struct tty_struct *tty, struct serial_struct *ss)
 	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)) {
@@ -1386,8 +1385,6 @@ static int rs_open(struct tty_struct *tty, struct file * filp)
 	tty->driver_data = info;
 	tty->port = port;
 
-	port->low_latency = (port->flags & ASYNC_LOW_LATENCY) ? 1 : 0;
-
 	retval = startup(tty, info);
 	if (retval) {
 		return retval;

drivers/tty/hvc/hvcs.c

@@ -605,7 +605,7 @@ static int hvcs_io(struct hvcs_struct *hvcsd)
 		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

@@ -101,7 +101,6 @@ static int ipw_open(struct tty_struct *linux_tty, struct file *filp)
 
 	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

@@ -1273,7 +1273,6 @@ static int mxser_set_serial_info(struct tty_struct *tty,
 				(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

@@ -565,9 +565,6 @@ static int ifx_port_activate(struct tty_port *port, struct tty_struct *tty)
 	/* 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

@@ -521,9 +521,6 @@ max3100_set_termios(struct uart_port *port, struct ktermios *termios,
 			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

@@ -975,7 +975,6 @@ static int uart_set_info(struct tty_struct *tty, struct tty_port *port,
 	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;
@@ -1795,8 +1794,6 @@ static int uart_port_activate(struct tty_port *port, struct tty_struct *tty)
 	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

@@ -672,7 +672,6 @@ static int open(struct tty_struct *tty, struct file *filp)
 	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

@@ -240,8 +240,7 @@ struct tty_port {
 	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 */