Re: [PATCH 1/3] serial: 8250: Handle UART without interrupt on TEMT using em485
From: Jiri Slaby
Date: Fri Jan 29 2021 - 02:24:32 EST
On 29. 01. 21, 0:36, Eric Tremblay wrote:
The patch introduce the UART_CAP_TEMT capability which is by default
assigned to all 8250 UART since the code assume that device has the
interrupt on TEMT
In the case where the device does not support it, we calculate the
maximum of time it could take for the transmitter to empty the
shift register. When we get in the situation where we get the
THRE interrupt but the TEMT bit is not set we start the timer
and recall __stop_tx after the delay
Signed-off-by: Eric Tremblay <etremblay@xxxxxxxxxxxxxxxxxxxx>
---
drivers/tty/serial/8250/8250.h | 1 +
drivers/tty/serial/8250/8250_bcm2835aux.c | 2 +-
drivers/tty/serial/8250/8250_omap.c | 2 +-
drivers/tty/serial/8250/8250_port.c | 89 ++++++++++++++++++++++-
include/linux/serial_8250.h | 2 +
5 files changed, 93 insertions(+), 3 deletions(-)
diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index 52bb21205bb6..5361b761eed7 100644
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -82,6 +82,7 @@ struct serial8250_config {
#define UART_CAP_MINI (1 << 17) /* Mini UART on BCM283X family lacks:
* STOP PARITY EPAR SPAR WLEN5 WLEN6
*/
+#define UART_CAP_TEMT (1 << 18) /* UART have interrupt on TEMT */
What about the inversion _NOTEMT? You then set it only on uarts without
TEMT and don't need to update every single driver.
diff --git a/drivers/tty/serial/8250/8250_bcm2835aux.c b/drivers/tty/serial/8250/8250_bcm2835aux.c
index fd95860cd661..354faebce885 100644
--- a/drivers/tty/serial/8250/8250_bcm2835aux.c
+++ b/drivers/tty/serial/8250/8250_bcm2835aux.c
@@ -91,7 +91,7 @@ static int bcm2835aux_serial_probe(struct platform_device *pdev)
return -ENOMEM;
/* initialize data */
- up.capabilities = UART_CAP_FIFO | UART_CAP_MINI;
+ data->uart.capabilities = UART_CAP_FIFO | UART_CAP_MINI | UART_CAP_TEMT;
This change looks weird and undocumented. Why do you set data->uart
suddenly?
Actually, does this build?
up.port.dev = &pdev->dev;
up.port.regshift = 2;
up.port.type = PORT_16550;
diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
index 23e0decde33e..1c21ac68ff37 100644
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -1294,7 +1294,7 @@ static int omap8250_probe(struct platform_device *pdev)
up.port.regshift = 2;
up.port.fifosize = 64;
up.tx_loadsz = 64;
- up.capabilities = UART_CAP_FIFO;
+ up.capabilities = UART_CAP_FIFO | UART_CAP_TEMT;
#ifdef CONFIG_PM
/*
* Runtime PM is mostly transparent. However to do it right we need to a
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index b0af13074cd3..44a54406e4b4 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -558,8 +558,41 @@ 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;
+
+ /* byte size and parity */
+ switch (cflag & CSIZE) {
+ case CS5:
+ bits = 7;
+ break;
+ case CS6:
+ bits = 8;
+ break;
+ case CS7:
+ bits = 9;
+ break;
+ default:
+ bits = 10;
+ break; /* CS8 */
+ }
+
+ if (cflag & CSTOPB)
+ bits++;
+ if (cflag & PARENB)
+ bits++;
+
+ p->em485->no_temt_delay = bits*1000000/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)
{
@@ -618,6 +651,18 @@ 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_TEMT)) {
+ struct tty_struct *tty = p->port.state->port.tty;
Is this safe? Don't you need a tty reference? Or maybe you need to pass
the tty from the TIOCSRS485 ioctl to here.
+ 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;
@@ -649,6 +694,7 @@ 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;
@@ -1494,6 +1540,15 @@ static void start_hrtimer_ms(struct hrtimer *hrt, unsigned long msec)
hrtimer_start(hrt, t, HRTIMER_MODE_REL);
}
+static void start_hrtimer_us(struct hrtimer *hrt, unsigned long usec)
+{
+ long sec = usec / 1000000;
+ long nsec = (usec % 1000000) * 1000;
+ ktime_t t = ktime_set(sec, nsec);
Why not ns_to_ktime without all those divisions?
+
+ hrtimer_start(hrt, t, HRTIMER_MODE_REL);
+}
+
static void __stop_tx_rs485(struct uart_8250_port *p)
{
struct uart_8250_em485 *em485 = p->em485;
@@ -1531,8 +1586,18 @@ static inline void __stop_tx(struct uart_8250_port *p)
* shift register are empty. It is for device driver to enable
* interrupt on TEMT.
*/
- if ((lsr & BOTH_EMPTY) != BOTH_EMPTY)
+ if ((lsr & BOTH_EMPTY) != BOTH_EMPTY) {
+ /*
+ * On devices with no interrupt on TEMT available
+ * start a timer for a byte time, the timer will recall
+ * __stop_tx
+ */
+ if (!(p->capabilities & UART_CAP_TEMT) && (lsr & UART_LSR_THRE)) {
+ em485->active_timer = &em485->no_temt_timer;
How does this interfere with the current handling of active_timer? You
should explain the changed functionality in the commit log. And you
don't reset it to NULL in the timer.
+ start_hrtimer_us(&em485->no_temt_timer, em485->no_temt_delay);
+ }
return;
+ }
__stop_tx_rs485(p);
}
@@ -1631,6 +1696,25 @@ 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)
+ __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;
@@ -2792,6 +2876,9 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
serial8250_set_divisor(port, baud, quot, frac);
+ if (!(up->capabilities & UART_CAP_TEMT))
+ 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.
diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
index 9e655055112d..d2c66faff0dd 100644
--- a/include/linux/serial_8250.h
+++ b/include/linux/serial_8250.h
@@ -79,7 +79,9 @@ 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 tempt interrupt" timer */
struct hrtimer *active_timer; /* pointer to active timer */
+ unsigned int no_temt_delay; /* Value of delay for no TEMT UART */
struct uart_8250_port *port; /* for hrtimer callbacks */
unsigned int tx_stopped:1; /* tx is currently stopped */
};
--
js
suse labs