linux-kernel - [PATCH] [90/106] serial/imx: read cts state only after acking cts change irq

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Date:	Tue, 26 Apr 2011 14:14:12 -0700 (PDT)
From:	Andi Kleen <andi@...stfloor.org>
To:	u.kleine-koenig@...gutronix.de, Arwed.Springer@...trumpf.com,
	gregkh@...e.de, ak@...ux.intel.com, linux-kernel@...r.kernel.org,
	stable@...nel.org, tim.bird@...sony.com
Subject: [PATCH] [90/106] serial/imx: read cts state only after acking cts change irq

2.6.35-longterm review patch.  If anyone has any objections, please let me 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uart_handle_cts_change is called with a outdated value for cts.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>
Signed-off-by: Andi Kleen <ak@...ux.intel.com>

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

Index: linux-2.6.35.y/drivers/serial/imx.c
===================================================================
--- linux-2.6.35.y.orig/drivers/serial/imx.c
+++ linux-2.6.35.y/drivers/serial/imx.c
@@ -383,12 +383,13 @@ 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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