serial: core: introduce uart_port_tx_flags()

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: stable <stable@kernel.org>
Tested-by: Emil Kronborg <emil.kronborg@protonmail.com>
Link: https://lore.kernel.org/r/20240201105557.28043-1-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 536b2581d3e2007593323a53c050d037d6ac5dd1..55b1f3ba48ac1725f110747b8d05ce6bbfc1de0b 100644 (file)
--- 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.
  */