Patchwork [3.5.y.z,extended,stable] Patch "serial/mxs-auart: increase time to wait for transmitter to" has been added to staging queue

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Submitter Luis Henriques
Date Aug. 4, 2013, 9:49 a.m.
Message ID <1375609765-10989-1-git-send-email-luis.henriques@canonical.com>
Download mbox | patch
Permalink /patch/264485/
State New
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Luis Henriques - Aug. 4, 2013, 9:49 a.m.
This is a note to let you know that I have just added a patch titled

    serial/mxs-auart: increase time to wait for transmitter to

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

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From cc59f4b29c6a70eb6f51920fb0103e016f5b276f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= <u.kleine-koenig@pengutronix.de>
Date: Fri, 28 Jun 2013 11:49:41 +0200
Subject: [PATCH] serial/mxs-auart: increase time to wait for transmitter to
 become idle
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

commit 079a036f4283e2b0e5c26080b8c5112bc0cc1831 upstream.

Without this patch the driver waits ~1 ms for the UART to become idle. At
115200n8 this time is (theoretically) enough to transfer 11.5 characters
(= 115200 bits/s / (10 Bits/char) * 1ms). As the mxs-auart has a fifo size
of 16 characters the clock is gated too early. The problem is worse for
lower baud rates.

This only happens to really shut down the transmitter in the middle of a
transfer if /dev/ttyAPPx isn't opened in userspace (e.g. by a getty) but
was at least once (because the bootloader doesn't disable the transmitter).

So increase the timeout to 20 ms which should be enough for 9600n8, too.
Moreover skip gating the clock if the timeout is elapsed.

Signed-off-by: Uwe Kleine-K├Ânig <u.kleine-koenig@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[ luis: backported to 3.5: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
 drivers/tty/serial/mxs-auart.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

--
1.8.3.2

Patch

diff --git a/drivers/tty/serial/mxs-auart.c b/drivers/tty/serial/mxs-auart.c
index 4313f49..64565f8 100644
--- a/drivers/tty/serial/mxs-auart.c
+++ b/drivers/tty/serial/mxs-auart.c
@@ -545,7 +545,7 @@  auart_console_write(struct console *co, const char *str, unsigned int count)
 	struct mxs_auart_port *s;
 	struct uart_port *port;
 	unsigned int old_ctrl0, old_ctrl2;
-	unsigned int to = 1000;
+	unsigned int to = 20000;

 	if (co->index >	MXS_AUART_PORTS || co->index < 0)
 		return;
@@ -566,18 +566,23 @@  auart_console_write(struct console *co, const char *str, unsigned int count)

 	uart_console_write(port, str, count, mxs_auart_console_putchar);

-	/*
-	 * Finally, wait for transmitter to become empty
-	 * and restore the TCR
-	 */
+	/* Finally, wait for transmitter to become empty ... */
 	while (readl(port->membase + AUART_STAT) & AUART_STAT_BUSY) {
+		udelay(1);
 		if (!to--)
 			break;
-		udelay(1);
 	}

-	writel(old_ctrl0, port->membase + AUART_CTRL0);
-	writel(old_ctrl2, port->membase + AUART_CTRL2);
+	/*
+	 * ... and restore the TCR if we waited long enough for the transmitter
+	 * to be idle. This might keep the transmitter enabled although it is
+	 * unused, but that is better than to disable it while it is still
+	 * transmitting.
+	 */
+	if (!(readl(port->membase + AUART_STAT) & AUART_STAT_BUSY)) {
+		writel(old_ctrl0, port->membase + AUART_CTRL0);
+		writel(old_ctrl2, port->membase + AUART_CTRL2);
+	}

 	clk_disable(s->clk);
 }