linux-kernel - [34-longterm 092/196] serial/imx: read cts state only after acking cts change irq

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Message-Id: <1331598109-31424-47-git-send-email-paul.gortmaker@windriver.com>
Date:	Mon, 12 Mar 2012 20:20:05 -0400
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	stable@...nel.org, linux-kernel@...r.kernel.org
Cc:	stable-review@...nel.org,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: [34-longterm 092/196] serial/imx: read cts state only after acking cts change irq

From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>

                   -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    If you see a problem with using this for longterm, please comment.
                   -------------------

commit 5680e94148a86e8c31fdc5cb0ea0d5c6810c05b0 upstream.

If cts changes between reading the level at the cts input (USR1_RTSS)
and acking the irq (USR1_RTSD) the last edge doesn't generate an irq and
uart_handle_cts_change is called with a outdated value for cts.

The race was introduced by commit

	ceca629 ([ARM] 2971/1: i.MX uart handle rts irq)

[PG: file in drivers/serial not drivers/tty/serial in .34]

Reported-by: Arwed Springer <Arwed.Springer@...trumpf.com>
Tested-by: Arwed Springer <Arwed.Springer@...trumpf.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
---
 drivers/serial/imx.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/serial/imx.c b/drivers/serial/imx.c
index eacb588..6d2028e 100644
--- a/drivers/serial/imx.c
+++ b/drivers/serial/imx.c
@@ -383,12 +383,13 @@ static void imx_start_tx(struct uart_port *port)
 static irqreturn_t imx_rtsint(int irq, void *dev_id)
 {
 	struct imx_port *sport = dev_id;
-	unsigned int val = readl(sport->port.membase + USR1) & USR1_RTSS;
+	unsigned int val;
 	unsigned long flags;
 
 	spin_lock_irqsave(&sport->port.lock, flags);
 
 	writel(USR1_RTSD, sport->port.membase + USR1);
+	val = readl(sport->port.membase + USR1) & USR1_RTSS;
 	uart_handle_cts_change(&sport->port, !!val);
 	wake_up_interruptible(&sport->port.state->port.delta_msr_wait);
 
-- 
1.7.9.3

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