linux-kernel - [21/55] serial/imx: read cts state only after acking cts change irq

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Message-Id: <20110429185654.601769517@clark.kroah.org>
Date:	Fri, 29 Apr 2011 11:55:44 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Uwe Kleine-KÃ¶nig 
	<u.kleine-koenig@...gutronix.de>
Subject: [21/55] serial/imx: read cts state only after acking cts change irq

2.6.38-stable review patch.  If anyone has any objections, please let us know.

------------------

From: =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= <u.kleine-koenig@...gutronix.de>

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uart_handle_cts_change is called with a outdated value for cts.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)

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>

---
 drivers/tty/serial/imx.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -382,12 +382,13 @@ static void imx_start_tx(struct uart_por
 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);
 


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