[PATCH] ARM: imx serial driver: fix resume

Daniel Mack daniel at caiaq.de
Wed Oct 6 12:57:16 EDT 2010

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

I just came across a bug in the IMX31 serial driver which is still
present in the newest kernels and which prevents successful
resume-operation for the IMX31 serial ports.

What happens is that in "drivers/serial/imx.c" on resume function
"serial_imx_resume" gets called. This function in turn calls
"uart_resume_port" (in the generic serial driver "serial_core.c"),
which in turn calls "imx_start_tx" in "imx.c" (in case the SIO-port
was really suspended) which in turn calls "imx_transmit_buffer".

However calling "imx_transmit_buffer" with an empty TX-fifo (as is
usually the case) will result in the serial port starting to transmit
(actually the old [already sent] tx-buffer), as there is no check if
the tx-buffer is empty before starting to feed tx-fifo-data to the
serial port hardware.

Signed-off-by: Volker Ernst <volker.ernst at txtr.com>
Cc: Daniel Mack <daniel at caiaq.de>
Cc: Andy Green <andy at warmcat.com>

Volker did all the work on this, he just doesn't want to push his great
contributions upstream, so I do it for him :)

 drivers/serial/imx.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/serial/imx.c b/drivers/serial/imx.c
index 66ecc7a..0170119 100644
--- a/drivers/serial/imx.c
+++ b/drivers/serial/imx.c
@@ -328,13 +328,13 @@ 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)) {
+		if (uart_circ_empty(xmit))
+			break;
 		/* 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);
-		if (uart_circ_empty(xmit))
-			break;
 	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)

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