[PATCH] serial/imx: check that the buffer is non-empty before sending it out

[Uwe Kleine-König]

From: Volker Ernst <volker.ernst at txtr.com>

The .start_tx callback (imx_start_tx here) isn't only called when the
buffer is non-empty.  E.g. after resume or when handshaking is enabled
and the other side starts to signal being ready.

So check for an empty puffer already before sending the first character.
This prevents sending out stale (or uninitialised) data.

Signed-off-by: Volker Ernst <volker.ernst at txtr.com>
Signed-off-by: Daniel Mack <daniel at caiaq.de>
Cc: Andy Green <andy at warmcat.com>
[ukl: reword commit log, put check in while condition]
Signed-off-by: Uwe Kleine-König <u.kleine-koenig at pengutronix.de>
---
Hello,

as I didn't sent a patch, here comes my current version.  Don't know if
it makes it easier to test for you ...

I faked Daniel's SoB as Andrew said he did, compressed the changelog a
bit and put the check in the while condition as I suggested.

Best regards
Uwe

 drivers/serial/imx.c |    5 ++---
 1 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/serial/imx.c b/drivers/serial/imx.c
index 66ecc7a..dfcf4b1 100644
--- a/drivers/serial/imx.c
+++ b/drivers/serial/imx.c
@@ -327,14 +327,13 @@ static inline void imx_transmit_buffer(struct imx_port *sport)
 {
 	struct circ_buf *xmit = &sport->port.state->xmit;
 
-	while (!(readl(sport->port.membase + UTS) & UTS_TXFULL)) {
+	while (!uart_circ_empty(xmit) &&
+			!(readl(sport->port.membase + UTS) & UTS_TXFULL)) {
 		/* send xmit->buf[xmit->tail]
 		 * out the port here */
 		writel(xmit->buf[xmit->tail], sport->port.membase + URTX0);
 		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
 		sport->port.icount.tx++;
-		if (uart_circ_empty(xmit))
-			break;
 	}
 
 	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
-- 
1.7.2.3