Commit 7a107b2c authored by Ilpo Järvinen's avatar Ilpo Järvinen Committed by Greg Kroah-Hartman
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Revert "serial: 8250: Handle UART without interrupt on TEMT using em485" 

This partially reverts commit f6f58610. The code added by
that commit containted math overflow for 32-bit archs. In
addition, the approach used in it is unnecessarily complicated
requiring a dedicated timer just for notemt. A simpler approach
for providing UART_CAP_NOTEMT already exists (patches 1-2):
  https://lore.kernel.org/linux-serial/20220411083321.9131-3-ilpo.jarvinen@linux.intel.com/T/#u


Thus, simply revert the UART_CAP_NOTEMT change for now.

There were two driver changes within the patch series adding
UART_CAP_NOTEMT taking advantage of the newly added flag.
This does not revert the driver changes and therefore also
UART_CAP_NOTEMT define has to remain. UART_CAP_NOTEMT remains
no-op until support is again added.

Fixes: f6f58610 ("serial: 8250: Handle UART without interrupt on TEMT using em485")
Signed-off-by: default avatarIlpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/5f874142-fb1f-bff7-f33-fac823e65e2e@linux.intel.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 2a72b1b2

drivers/tty/serial/8250/8250_port.c

+2 −74
Original line number Diff line number Diff line
@@ -571,21 +571,8 @@ static void serial8250_clear_fifos(struct uart_8250_port *p) 
	}

}



static inline void serial8250_em485_update_temt_delay(struct uart_8250_port *p,

			unsigned int cflag, unsigned int baud)

{

	unsigned int bits;



	if (!p->em485)

		return;



	bits = tty_get_frame_size(cflag);

	p->em485->no_temt_delay = DIV_ROUND_UP(bits * NSEC_PER_SEC, baud);

}



static enum hrtimer_restart serial8250_em485_handle_start_tx(struct hrtimer *t);

static enum hrtimer_restart serial8250_em485_handle_stop_tx(struct hrtimer *t);

static enum hrtimer_restart serial8250_em485_handle_no_temt(struct hrtimer *t);



void serial8250_clear_and_reinit_fifos(struct uart_8250_port *p)

{
@@ -644,16 +631,6 @@ static int serial8250_em485_init(struct uart_8250_port *p) 
		     HRTIMER_MODE_REL);

	hrtimer_init(&p->em485->start_tx_timer, CLOCK_MONOTONIC,

		     HRTIMER_MODE_REL);



	if (p->capabilities & UART_CAP_NOTEMT) {

		struct tty_struct *tty = p->port.state->port.tty;



		serial8250_em485_update_temt_delay(p, tty->termios.c_cflag,

						   tty_get_baud_rate(tty));

		hrtimer_init(&p->em485->no_temt_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);

		p->em485->no_temt_timer.function = &serial8250_em485_handle_no_temt;

	}



	p->em485->stop_tx_timer.function = &serial8250_em485_handle_stop_tx;

	p->em485->start_tx_timer.function = &serial8250_em485_handle_start_tx;

	p->em485->port = p;
@@ -685,7 +662,6 @@ void serial8250_em485_destroy(struct uart_8250_port *p) 


	hrtimer_cancel(&p->em485->start_tx_timer);

	hrtimer_cancel(&p->em485->stop_tx_timer);

	hrtimer_cancel(&p->em485->no_temt_timer);



	kfree(p->em485);

	p->em485 = NULL;
@@ -1528,11 +1504,6 @@ static void start_hrtimer_ms(struct hrtimer *hrt, unsigned long msec) 
	hrtimer_start(hrt, ms_to_ktime(msec), HRTIMER_MODE_REL);

}



static void start_hrtimer_ns(struct hrtimer *hrt, unsigned long nsec)

{

	hrtimer_start(hrt, ns_to_ktime(nsec), HRTIMER_MODE_REL);

}



static void __stop_tx_rs485(struct uart_8250_port *p)

{

	struct uart_8250_em485 *em485 = p->em485;
@@ -1564,33 +1535,14 @@ static inline void __stop_tx(struct uart_8250_port *p) 


	if (em485) {

		unsigned char lsr = serial_in(p, UART_LSR);



		p->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS;



		/*

		 * To provide required timing and allow FIFO transfer,

		 * To provide required timeing and allow FIFO transfer,

		 * __stop_tx_rs485() must be called only when both FIFO and

		 * shift register are empty. It is for device driver to enable

		 * interrupt on TEMT.

		 */

		if ((lsr & BOTH_EMPTY) != BOTH_EMPTY) {

			if (!(p->capabilities & UART_CAP_NOTEMT))

				/* __stop_tx will be called again once TEMT triggers */

				return;



			if (!(lsr & UART_LSR_THRE))

				/* __stop_tx will be called again once THRE triggers */

				return;



			/*

			 * On devices with no TEMT interrupt available, start

			 * a timer for a byte time. The timer will recall

			 * __stop_tx().

			 */

			em485->active_timer = &em485->no_temt_timer;

			start_hrtimer_ns(&em485->no_temt_timer, em485->no_temt_delay);

		if ((lsr & BOTH_EMPTY) != BOTH_EMPTY)

			return;

		}



		__stop_tx_rs485(p);

	}
@@ -1701,27 +1653,6 @@ static inline void start_tx_rs485(struct uart_port *port) 
	__start_tx(port);

}



static enum hrtimer_restart serial8250_em485_handle_no_temt(struct hrtimer *t)

{

	struct uart_8250_em485 *em485;

	struct uart_8250_port *p;

	unsigned long flags;



	em485 = container_of(t, struct uart_8250_em485, no_temt_timer);

	p = em485->port;



	serial8250_rpm_get(p);

	spin_lock_irqsave(&p->port.lock, flags);

	if (em485->active_timer == &em485->no_temt_timer) {

		em485->active_timer = NULL;

		__stop_tx(p);

	}



	spin_unlock_irqrestore(&p->port.lock, flags);

	serial8250_rpm_put(p);

	return HRTIMER_NORESTART;

}



static enum hrtimer_restart serial8250_em485_handle_start_tx(struct hrtimer *t)

{

	struct uart_8250_em485 *em485 = container_of(t, struct uart_8250_em485,
@@ -2927,9 +2858,6 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios, 


	serial8250_set_divisor(port, baud, quot, frac);



	if (up->capabilities & UART_CAP_NOTEMT)

		serial8250_em485_update_temt_delay(up, termios->c_cflag, baud);



	/*

	 * LCR DLAB must be set to enable 64-byte FIFO mode. If the FCR

	 * is written without DLAB set, this mode will be disabled.

include/linux/serial_8250.h

+0 −2
Original line number Diff line number Diff line
@@ -79,9 +79,7 @@ struct uart_8250_ops { 
struct uart_8250_em485 {

	struct hrtimer		start_tx_timer; /* "rs485 start tx" timer */

	struct hrtimer		stop_tx_timer;  /* "rs485 stop tx" timer */

	struct hrtimer		no_temt_timer;  /* "rs485 no TEMT interrupt" timer */

	struct hrtimer		*active_timer;  /* pointer to active timer */

	unsigned long		no_temt_delay;  /* Delay for no_temt_timer */

	struct uart_8250_port	*port;          /* for hrtimer callbacks */

	unsigned int		tx_stopped:1;	/* tx is currently stopped */

};