[PATCH 1/2] serial: core: introduce uart_port_tx_flags()

[PATCH 1/2] serial: core: introduce uart_port_tx_flags()

[Jiri Slaby (SUSE)]

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) <jirislaby@kernel.org>
Cc: Emil Kronborg <emil.kronborg@protonmail.com>
---
 include/linux/serial_core.h | 32 +++++++++++++++++++++++++++-----
 1 file changed, 27 insertions(+), 5 deletions(-)

diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 536b2581d3e2..edefb6d73604 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -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

[PATCH 2/2] serial: mxs-auart: fix tx

[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().

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) <jirislaby@kernel.org>
Reported-by: Emil Kronborg <emil.kronborg@protonmail.com>
Fixes: 2d141e683e9a ("tty: serial: use uart_port_tx() helper")
Closes: https://lore.kernel.org/all/miwgbnvy3hjpnricubg76ytpn7xoceehwahupy25bubbduu23s@om2lptpa26xw/
---
 drivers/tty/serial/mxs-auart.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/mxs-auart.c b/drivers/tty/serial/mxs-auart.c
index 3ec725555bcc..4749331fe618 100644
--- a/drivers/tty/serial/mxs-auart.c
+++ b/drivers/tty/serial/mxs-auart.c
@@ -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

Re: [PATCH 1/2] serial: core: introduce uart_port_tx_flags()

[Jiri Slaby]

On 31. 01. 24, 13:13, Jiri Slaby (SUSE) wrote:
> 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) <jirislaby@kernel.org>
> Cc: Emil Kronborg <emil.kronborg@protonmail.com>
> ---
>   include/linux/serial_core.h | 32 +++++++++++++++++++++++++++-----
>   1 file changed, 27 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
> index 536b2581d3e2..edefb6d73604 100644
> --- a/include/linux/serial_core.h
> +++ b/include/linux/serial_core.h
> @@ -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)		      \

Hold on, this is obviously inverted!

-- 
js
suse labs