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Revert "serial: 8250: Handle UART without interrupt on TEMT using em485" 

This partially reverts commit f6f586102a. 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: f6f586102a ("serial: 8250: Handle UART without interrupt on TEMT using em485")
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/5f874142-fb1f-bff7-f33-fac823e65e2e@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ilpo Järvinen 2022-04-20 11:19:01 +03:00 committed by Greg Kroah-Hartman
parent 2a72b1b2db
commit 7a107b2c6b
2 changed files with 2 additions and 76 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

76
drivers/tty/serial/8250/8250_port.c
View File

@ -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.

2
include/linux/serial_8250.h
View File

@ -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 */
};