[PATCH v2 RESEND 1/3] serial: Create uart_xmit_advance()

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

A very common pattern in the drivers is to advance xmit tail
index and do bookkeeping of Tx'ed characters. Create
uart_xmit_advance() to handle it.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
---
 include/linux/serial_core.h | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index aef3145f2032..ffc7b8cb7a7f 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -616,6 +616,23 @@ struct uart_state {
 /* number of characters left in xmit buffer before we ask for more */
 #define WAKEUP_CHARS		256
 
+/**
+ * uart_xmit_advance - Advance xmit buffer and account Tx'ed chars
+ * @up: uart_port structure describing the port
+ * @chars: number of characters sent
+ *
+ * This function advances the tail of circular xmit buffer by the number of
+ * @chars transmitted and handles accounting of transmitted bytes (into
+ * @up's icount.tx).
+ */
+static inline void uart_xmit_advance(struct uart_port *up, unsigned int chars)
+{
+	struct circ_buf *xmit = &up->state->xmit;
+
+	xmit->tail = (xmit->tail + chars) & (UART_XMIT_SIZE - 1);
+	up->icount.tx += chars;
+}
+
 struct module;
 struct tty_driver;
 
-- 
2.30.2