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Commit 7efd0da2 authored by Mischa Jonker's avatar Mischa Jonker Committed by Vineet Gupta
Browse files

ARC: Fix __udelay calculation 



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: default avatarMischa Jonker <mjonker@synopsys.com>
Signed-off-by: default avatarVineet Gupta <vgupta@synopsys.com>
parent 8508d565

arch/arc/include/asm/delay.h

+2 −3
Original line number Diff line number Diff line
@@ -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);

}