Add UART_CAP_NOTEMT for UARTs that lack interrupt on TEMT but
want to use em485. Em485 framework needs to ensure not only
FIFO is empty but also that tx shift register is empty.
This approach uses Uwe Kleine-König's suggestion on simply
using/incrementing stop_tx timer rather than adding another
timer. When UART_CAP_NOTEMT is set and THRE is present w/o
TEMT, stop tx timer is reused to wait for the emptying of
the shift register.
Suggested-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
Cc: Eric Tremblay <etremblay@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
---
drivers/tty/serial/8250/8250.h | 1 +
drivers/tty/serial/8250/8250_port.c | 28 +++++++++++++++++++---------
2 files changed, 20 insertions(+), 9 deletions(-)
diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index db784ace25d8..100426cd2335 100644
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -83,6 +83,7 @@ struct serial8250_config {
#define UART_CAP_MINI BIT(17) /* Mini UART on BCM283X family lacks:
* STOP PARITY EPAR SPAR WLEN5 WLEN6
*/
+#define UART_CAP_NOTEMT BIT(18) /* UART cannot interrupt on TEMT */
#define UART_BUG_QUOT BIT(0) /* UART has buggy quot LSB */
#define UART_BUG_TXEN BIT(1) /* UART has buggy TX IIR status */
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index d30a6c1c4c20..276c5281aaa0 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1504,18 +1504,19 @@ static void start_hrtimer_ms(struct hrtimer *hrt, unsigned long msec)
hrtimer_start(hrt, ms_to_ktime(msec), HRTIMER_MODE_REL);
}
-static void __stop_tx_rs485(struct uart_8250_port *p)
+static void __stop_tx_rs485(struct uart_8250_port *p, u64 stop_delay)
{
struct uart_8250_em485 *em485 = p->em485;
+ stop_delay += (u64)p->port.rs485.delay_rts_after_send * NSEC_PER_USEC;
+
/*
* rs485_stop_tx() is going to set RTS according to config
* AND flush RX FIFO if required.
*/
- if (p->port.rs485.delay_rts_after_send > 0) {
+ if (stop_delay > 0) {
em485->active_timer = &em485->stop_tx_timer;
- start_hrtimer_ms(&em485->stop_tx_timer,
- p->port.rs485.delay_rts_after_send);
+ hrtimer_start(&em485->stop_tx_timer, ns_to_ktime(stop_delay), HRTIMER_MODE_REL);
} else {
p->rs485_stop_tx(p);
em485->active_timer = NULL;
@@ -1535,16 +1536,25 @@ static inline void __stop_tx(struct uart_8250_port *p)
if (em485) {
unsigned char lsr = serial_in(p, UART_LSR);
+ u64 stop_delay = 0;
+
+ if (!(lsr & UART_LSR_THRE))
+ return;
/*
* 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.
+ * shift register are empty. The device driver should either
+ * enable interrupt on TEMT or set UART_CAP_NOTEMT that will
+ * enlarge stop_tx_timer by the tx time of one frame to cover
+ * for emptying of the shift register.
*/
- if ((lsr & BOTH_EMPTY) != BOTH_EMPTY)
- return;
+ if (!(lsr & UART_LSR_TEMT)) {
+ if (!(p->capabilities & UART_CAP_NOTEMT))
+ return;
+ stop_delay = p->port.frame_time;
+ }
- __stop_tx_rs485(p);
+ __stop_tx_rs485(p, stop_delay);
}
__do_stop_tx(p);
}
--
2.30.2
