linux-kernel - [ 13/50] ARC: Fix _

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Message-Id: <20131016174359.974775795@linuxfoundation.org>
Date:	Wed, 16 Oct 2013 10:44:59 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Mischa Jonker <mjonker@...opsys.com>,
	Vineet Gupta <vgupta@...opsys.com>
Subject: [ 13/50] ARC: Fix __udelay calculation

3.11-stable review patch.  If anyone has any objections, please let me know.

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

From: Mischa Jonker <mjonker@...opsys.com>

commit 7efd0da2d17360e1cef91507dbe619db0ee2c691 upstream.

Cast usecs to u64, to ensure that the (usecs * 4295 * HZ)
multiplication is 64 bit.

Initially, the (usecs * 4295 * HZ) part was done as a 32 bit
multiplication, with the result casted to 64 bit. This led to some bits
falling off, causing a "DMA initialization error" in the stmmac Ethernet
driver, due to a premature timeout.

Signed-off-by: Mischa Jonker <mjonker@...opsys.com>
Signed-off-by: Vineet Gupta <vgupta@...opsys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/arc/include/asm/delay.h |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

--- a/arch/arc/include/asm/delay.h
+++ b/arch/arc/include/asm/delay.h
@@ -53,11 +53,10 @@ static inline void __udelay(unsigned lon
 {
 	unsigned long loops;
 
-	/* (long long) cast ensures 64 bit MPY - real or emulated
+	/* (u64) cast ensures 64 bit MPY - real or emulated
 	 * HZ * 4295 is pre-evaluated by gcc - hence only 2 mpy ops
 	 */
-	loops = ((long long)(usecs * 4295 * HZ) *
-		 (long long)(loops_per_jiffy)) >> 32;
+	loops = ((u64) usecs * 4295 * HZ * loops_per_jiffy) >> 32;
 
 	__delay(loops);
 }


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