serial: core: introduce uart_port_tx_flags()

Emil reports:
After updating Linux on an i.MX28 board, serial communication over AUART broke. When I TX from the board and measure on the TX pin, it seems like the HW fifo is not emptied before the transmission is stopped.

MXS performs weird things with stop_tx(). The driver makes it conditional on uart_tx_stopped().

So the driver needs special handling. Pass the brand new UART_TX_NOSTOP to uart_port_tx_flags() and handle the stop on its own.

Signed-off-by Jiri Slaby (SUSE) <[email protected]>

Reported-by Emil Kronborg <[email protected]>

Fixes 2d141e683e9a ("tty: serial: use uart_port_tx() helper")

Closes https://lore.kernel.org/all/miwgbnvy3hjpnricubg76ytpn7xoceehwahupy25bubbduu23s@om2lptpa26xw/ open here

---
  drivers/tty/serial/mxs-auart.c | 5 ++++-
  1 file changed, 4 insertions(+), 1 deletion(-)

drivers/tty/serial/mxs-auart.c +4 -1

index 3ec725555bcc..4749331fe618 100644
@@ -605,13 +605,16 @@ static void mxs_auart_tx_chars(struct mxs_auart_port *s)
  		return;
  	}
 
-	pending = uart_port_tx(&s->port, ch,
+	pending = uart_port_tx_flags(&s->port, ch, UART_TX_NOSTOP,
  		!(mxs_read(s, REG_STAT) & AUART_STAT_TXFF),
  		mxs_write(ch, s, REG_DATA));
  	if (pending)
  		mxs_set(AUART_INTR_TXIEN, s, REG_INTR);
  	else
  		mxs_clr(AUART_INTR_TXIEN, s, REG_INTR);
+
+	if (uart_tx_stopped(&s->port))
+               mxs_auart_stop_tx(&s->port);
  }
 
  static void mxs_auart_rx_char(struct mxs_auart_port *s)

Quoted 9 lines · Jiri Slaby (SUSE)

Emil reports:
After updating Linux on an i.MX28 board, serial communication over AUART broke. When I TX from the board and measure on the TX pin, it seems like the HW fifo is not emptied before the transmission is stopped.

MXS performs weird things with stop_tx(). The driver makes it conditional on uart_tx_stopped().

Quoted 7 lines

So the driver needs special handling. Pass the brand new UART_TX_NOSTOP to uart_port_tx_flags() and handle the stop on its own.

Signed-off-by Jiri Slaby (SUSE) <[email protected]>

Reported-by Emil Kronborg <[email protected]>

Fixes 2d141e683e9a ("tty: serial: use uart_port_tx() helper")

Closes https://lore.kernel.org/all/miwgbnvy3hjpnricubg76ytpn7xoceehwahupy25bubbduu23s@om2lptpa26xw/ open here

Am I unable to send a proper patch anymore?

I forgot to add mxs+arm maintainers:
Cc: Shawn Guo <[email protected]>
Cc: Sascha Hauer <[email protected]>
Cc: Pengutronix Kernel Team <[email protected]>
Cc: Fabio Estevam <[email protected]>
Cc: NXP Linux Team <[email protected]>
Cc: [email protected]

I can resend with those fixed, if you prefer...

Quoted 9 lines

Emil reports:
   After updating Linux on an i.MX28 board, serial communication over AUART broke. When I TX from the board and measure on the TX pin, it seems like the HW fifo is not emptied before the transmission is stopped.

MXS performs weird things with stop_tx(). The driver makes it conditional on uart_tx_stopped().

Quoted 8 lines

So the driver needs special handling. Pass the brand new UART_TX_NOSTOP to uart_port_tx_flags() and handle the stop on its own.

Signed-off-by Jiri Slaby (SUSE) <[email protected]>

Reported-by Emil Kronborg <[email protected]>

Fixes 2d141e683e9a ("tty: serial: use uart_port_tx() helper")

Closes:
https://lore.kernel.org/all/miwgbnvy3hjpnricubg76ytpn7xoceehwahupy25bubbduu23s@om2lptpa26xw/

Emil reports:
After updating Linux on an i.MX28 board, serial communication over AUART broke. When I TX from the board and measure on the TX pin, it seems like the HW fifo is not emptied before the transmission is stopped.

MXS performs weird things with stop_tx(). The driver makes it conditional on uart_tx_stopped().

So the driver needs special handling. Pass the brand new UART_TX_NOSTOP to uart_port_tx_flags() and handle the stop on its own.

Signed-off-by Jiri Slaby (SUSE) <[email protected]>

Reported-by Emil Kronborg <[email protected]>

Fixes 2d141e683e9a ("tty: serial: use uart_port_tx() helper")

Closes https://lore.kernel.org/all/miwgbnvy3hjpnricubg76ytpn7xoceehwahupy25bubbduu23s@om2lptpa26xw/ open here

---
 drivers/tty/serial/mxs-auart.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

drivers/tty/serial/mxs-auart.c +4 -2

index 3ec725555bcc..4749331fe618 100644
@@ -605,13 +605,16 @@ static void mxs_auart_tx_chars(struct mxs_auart_port *s)
 		return;
 	}
 
-	pending = uart_port_tx(&s->port, ch,
+	pending = uart_port_tx_flags(&s->port, ch, UART_TX_NOSTOP,
 		!(mxs_read(s, REG_STAT) & AUART_STAT_TXFF),
 		mxs_write(ch, s, REG_DATA));
 	if (pending)
 		mxs_set(AUART_INTR_TXIEN, s, REG_INTR);
 	else
 		mxs_clr(AUART_INTR_TXIEN, s, REG_INTR);
+
+	if (uart_tx_stopped(&s->port))
+               mxs_auart_stop_tx(&s->port);
 }
 
 static void mxs_auart_rx_char(struct mxs_auart_port *s)
--

2.43.0

And an enum with a flag: UART_TX_NOSTOP. To NOT call __port->ops->stop_tx() when the circular buffer is empty. mxs-uart needs this (see the next patch).

Signed-off-by Jiri Slaby (SUSE) <[email protected]>

Cc Emil Kronborg <[email protected]>

---

Notes:
[v2] fix/invert the condition

 include/linux/serial_core.h | 32 +++++++++++++++++++++++++++-----
 1 file changed, 27 insertions(+), 5 deletions(-)

include/linux/serial_core.h +27 -6

index 536b2581d3e2..55b1f3ba48ac 100644
@@ -748,8 +748,17 @@ struct uart_driver {
 
 void uart_write_wakeup(struct uart_port *port);
 
-#define __uart_port_tx(uport, ch, tx_ready, put_char, tx_done, for_test,      \
-		for_post)						      \
+/**
+ * enum UART_TX_FLAGS -- flags for uart_port_tx_flags()
+ *
+ * @UART_TX_NOSTOP: don't call port->ops->stop_tx() on empty buffer
+ */
+enum UART_TX_FLAGS {
+	UART_TX_NOSTOP = BIT(0),
+};
+
+#define __uart_port_tx(uport, ch, flags, tx_ready, put_char, tx_done,	      \
+		       for_test, for_post)				      \
 ({									      \
 	struct uart_port *__port = (uport);				      \
 	struct circ_buf *xmit = &__port->state->xmit;			      \

@@ -777,7 +786,7 @@ void uart_write_wakeup(struct uart_port *port);
 	if (pending < WAKEUP_CHARS) {					      \
 		uart_write_wakeup(__port);				      \
 									      \
-		if (pending == 0)					      \
+		if (!((flags) & UART_TX_NOSTOP) && pending == 0)	      \
 			__port->ops->stop_tx(__port);			      \
 	}								      \
 									      \

@@ -812,7 +821,7 @@ void uart_write_wakeup(struct uart_port *port);
  */
 #define uart_port_tx_limited(port, ch, count, tx_ready, put_char, tx_done) ({ \
 	unsigned int __count = (count);					      \
-	__uart_port_tx(port, ch, tx_ready, put_char, tx_done, __count,	      \
+	__uart_port_tx(port, ch, 0, tx_ready, put_char, tx_done, __count,     \
 			__count--);					      \
 })
 

@@ -826,8 +835,21 @@ void uart_write_wakeup(struct uart_port *port);
  * See uart_port_tx_limited() for more details.
  */
 #define uart_port_tx(port, ch, tx_ready, put_char)			\
-	__uart_port_tx(port, ch, tx_ready, put_char, ({}), true, ({}))
+	__uart_port_tx(port, ch, 0, tx_ready, put_char, ({}), true, ({}))
+
 
+/**
+ * uart_port_tx_flags -- transmit helper for uart_port with flags
+ * @port: uart port
+ * @ch: variable to store a character to be written to the HW
+ * @flags: %UART_TX_NOSTOP or similar
+ * @tx_ready: can HW accept more data function
+ * @put_char: function to write a character
+ *
+ * See uart_port_tx_limited() for more details.
+ */
+#define uart_port_tx_flags(port, ch, flags, tx_ready, put_char)		\
+	__uart_port_tx(port, ch, flags, tx_ready, put_char, ({}), true, ({}))
 /*
  * Baud rate helpers.
  */
--

2.43.0