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fb833b1fbb
Commit215e362daf("ARM: 8306/1: loop_udelay: remove bogomips value limitation") tried to increase the bogomips limitation, but in doing so messed up udelay such that it always gives about a 5% error in the delay, even if we use a timer. The calculation is: loops = UDELAY_MULT * us_delay * ticks_per_jiffy >> UDELAY_SHIFT Originally, UDELAY_MULT was ((UL(2199023) * HZ) >> 11) and UDELAY_SHIFT 30. Assuming HZ=100, us_delay of 1000 and ticks_per_jiffy of 1660000 (eg, 166MHz timer, 1ms delay) this would calculate: ((UL(2199023) * HZ) >> 11) * 1000 * 1660000 >> 30 => 165999 With the new values of 2047 * HZ + 483648 * HZ / 1000000 and 31, we get: (2047 * HZ + 483648 * HZ / 1000000) * 1000 * 1660000 >> 31 => 158269 which is incorrect. This is due to a typo - correcting it gives: (2147 * HZ + 483648 * HZ / 1000000) * 1000 * 1660000 >> 31 => 165999 i.o.w, the original value. Fixes:215e362daf("ARM: 8306/1: loop_udelay: remove bogomips value limitation") Cc: <stable@vger.kernel.org> Reviewed-by: Nicolas Pitre <nico@linaro.org> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
73 lines
2.0 KiB
C
73 lines
2.0 KiB
C
/*
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* Copyright (C) 1995-2004 Russell King
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*
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* Delay routines, using a pre-computed "loops_per_second" value.
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*/
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#ifndef __ASM_ARM_DELAY_H
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#define __ASM_ARM_DELAY_H
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#include <asm/memory.h>
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#include <asm/param.h> /* HZ */
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#define MAX_UDELAY_MS 2
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#define UDELAY_MULT UL(2147 * HZ + 483648 * HZ / 1000000)
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#define UDELAY_SHIFT 31
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#ifndef __ASSEMBLY__
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struct delay_timer {
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unsigned long (*read_current_timer)(void);
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unsigned long freq;
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};
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extern struct arm_delay_ops {
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void (*delay)(unsigned long);
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void (*const_udelay)(unsigned long);
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void (*udelay)(unsigned long);
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unsigned long ticks_per_jiffy;
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} arm_delay_ops;
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#define __delay(n) arm_delay_ops.delay(n)
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/*
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* This function intentionally does not exist; if you see references to
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* it, it means that you're calling udelay() with an out of range value.
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*
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* With currently imposed limits, this means that we support a max delay
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* of 2000us. Further limits: HZ<=1000
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*/
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extern void __bad_udelay(void);
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/*
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* division by multiplication: you don't have to worry about
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* loss of precision.
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*
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* Use only for very small delays ( < 2 msec). Should probably use a
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* lookup table, really, as the multiplications take much too long with
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* short delays. This is a "reasonable" implementation, though (and the
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* first constant multiplications gets optimized away if the delay is
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* a constant)
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*/
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#define __udelay(n) arm_delay_ops.udelay(n)
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#define __const_udelay(n) arm_delay_ops.const_udelay(n)
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#define udelay(n) \
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(__builtin_constant_p(n) ? \
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((n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() : \
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__const_udelay((n) * UDELAY_MULT)) : \
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__udelay(n))
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/* Loop-based definitions for assembly code. */
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extern void __loop_delay(unsigned long loops);
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extern void __loop_udelay(unsigned long usecs);
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extern void __loop_const_udelay(unsigned long);
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/* Delay-loop timer registration. */
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#define ARCH_HAS_READ_CURRENT_TIMER
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extern void register_current_timer_delay(const struct delay_timer *timer);
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#endif /* __ASSEMBLY__ */
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#endif /* defined(_ARM_DELAY_H) */
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