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Subject[PATCH 3/4] serial: 8250: Handle case port doesn't have TEMT interrupt using em485.
Date
Some 8250 ports only have TEMT interrupt, so current implementation
can't work for ports without it. The only chance to make it work is to
loop-read on LSR register.

With NO TEMT interrupt check if both TEMT and THRE are set looping on
LSR register.

Signed-off-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
---
drivers/tty/serial/8250/8250.h | 2 +-
drivers/tty/serial/8250/8250_dw.c | 2 +-
drivers/tty/serial/8250/8250_omap.c | 2 +-
drivers/tty/serial/8250/8250_port.c | 26 ++++++++++++++++++--------
include/linux/serial_8250.h | 1 +
5 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index ebfb0bd5bef5..5c6ae5f69432 100644
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -136,7 +136,7 @@ void serial8250_rpm_put(struct uart_8250_port *p);
void serial8250_rpm_get_tx(struct uart_8250_port *p);
void serial8250_rpm_put_tx(struct uart_8250_port *p);

-int serial8250_em485_init(struct uart_8250_port *p);
+int serial8250_em485_init(struct uart_8250_port *p, bool has_temt_isr);
void serial8250_em485_destroy(struct uart_8250_port *p);

static inline void serial8250_out_MCR(struct uart_8250_port *up, int value)
diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index 0f8b4da03d4e..888280ff5451 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -330,7 +330,7 @@ static int dw8250_rs485_config(struct uart_port *p,
* are idempotent
*/
if (rs485->flags & SER_RS485_ENABLED) {
- int ret = serial8250_em485_init(up);
+ int ret = serial8250_em485_init(up, false);

if (ret) {
rs485->flags &= ~SER_RS485_ENABLED;
diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
index 624b501fd253..ab483c8b30c8 100644
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -725,7 +725,7 @@ static int omap_8250_rs485_config(struct uart_port *port,
* are idempotent
*/
if (rs485->flags & SER_RS485_ENABLED) {
- int ret = serial8250_em485_init(up);
+ int ret = serial8250_em485_init(up, true);

if (ret) {
rs485->flags &= ~SER_RS485_ENABLED;
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index c8c10b5ec6d6..8432445c80e5 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -602,15 +602,16 @@ EXPORT_SYMBOL_GPL(serial8250_rpm_put);
/**
* serial8250_em485_init() - put uart_8250_port into rs485 emulating
* @p: uart_8250_port port instance
+ * @p: bool specify if 8250 port has TEMT interrupt or not
*
* The function is used to start rs485 software emulating on the
* &struct uart_8250_port* @p. Namely, RTS is switched before/after
* transmission. The function is idempotent, so it is safe to call it
* multiple times.
*
- * The caller MUST enable interrupt on empty shift register before
- * calling serial8250_em485_init(). This interrupt is not a part of
- * 8250 standard, but implementation defined.
+ * If has_temt_isr is passed as true, the caller MUST enable interrupt
+ * on empty shift register before calling serial8250_em485_init().
+ * This interrupt is not a part of 8250 standard, but implementation defined.
*
* The function is supposed to be called from .rs485_config callback
* or from any other callback protected with p->port.lock spinlock.
@@ -619,7 +620,7 @@ EXPORT_SYMBOL_GPL(serial8250_rpm_put);
*
* Return 0 - success, -errno - otherwise
*/
-int serial8250_em485_init(struct uart_8250_port *p)
+int serial8250_em485_init(struct uart_8250_port *p, bool has_temt_isr)
{
if (p->em485)
return 0;
@@ -636,6 +637,7 @@ int serial8250_em485_init(struct uart_8250_port *p)
p->em485->start_tx_timer.function = &serial8250_em485_handle_start_tx;
p->em485->port = p;
p->em485->active_timer = NULL;
+ p->em485->has_temt_isr = has_temt_isr;
serial8250_em485_rts_after_send(p);

return 0;
@@ -1520,11 +1522,19 @@ static inline void __stop_tx(struct uart_8250_port *p)
/*
* 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. If 8250 port supports it,
+ * it is for device driver to enable interrupt on TEMT.
+ * Otherwise must loop-read until TEMT and THRE flags are set.
*/
- if ((lsr & BOTH_EMPTY) != BOTH_EMPTY)
- return;
+ if (em485->has_temt_isr) {
+ if ((lsr & BOTH_EMPTY) != BOTH_EMPTY)
+ return;
+ } else {
+ while ((lsr & BOTH_EMPTY) != BOTH_EMPTY) {
+ lsr = serial_in(p, UART_LSR);
+ cpu_relax();
+ }
+ }

em485->active_timer = NULL;

diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
index a27ef5f56431..9b13cf59726b 100644
--- a/include/linux/serial_8250.h
+++ b/include/linux/serial_8250.h
@@ -83,6 +83,7 @@ struct uart_8250_em485 {
struct hrtimer start_tx_timer; /* "rs485 start tx" timer */
struct hrtimer stop_tx_timer; /* "rs485 stop tx" timer */
struct hrtimer *active_timer; /* pointer to active timer */
+ bool has_temt_isr; /* say if 8250 has TEMT interrupt or no */
struct uart_8250_port *port; /* for hrtimer callbacks */
};

--
2.17.1
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