| From | Greg Kroah-Hartman <> | Subject | [ 13/50] ARC: Fix __udelay calculation | Date | Wed, 16 Oct 2013 10:44:59 -0700 |
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3.11-stable review patch. If anyone has any objections, please let me know.
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From: Mischa Jonker <mjonker@synopsys.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@synopsys.com> Signed-off-by: Vineet Gupta <vgupta@synopsys.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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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