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ARC: Fix __udelay calculation

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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@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Mischa Jonker 2013-08-30 11:56:25 +02:00 committed by Greg Kroah-Hartman
parent 98f745546b
commit 8036c31c84
1 changed files with 2 additions and 3 deletions
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5
arch/arc/include/asm/delay.h
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@ -53,11 +53,10 @@ static inline void __udelay(unsigned long usecs)
{
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);
}