Commits
Russell King committed fb833b1fbb6
ARM: fix delays
Commit 215e362dafed ("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: 215e362dafed ("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>