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Explain where the value for UDELAY_MULT and UDELAY_SHIFT come from.
Also fix/clarify some comments pertaining to their usage in the
assembly code.
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
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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>
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Now that we don't support ARMv3 anymore, the loop based delay code can
convert microsecs into number of loops using a 64-bit multiplication
and more precision.
This allows us to lift the hard limit of 3355 on the bogomips value as
loops_per_jiffy may now safely span the full 32-bit range.
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
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Commit 70264367a243 ("ARM: 7653/2: do not scale loops_per_jiffy when
using a constant delay clock") fixed a problem with our timer-based
delay loop, where loops_per_jiffy is scaled by cpufreq yet used directly
by the timer delay ops.
This patch fixes the problem in a more elegant way by keeping a private
ticks_per_jiffy field in the delay ops, independent of loops_per_jiffy
and therefore not subject to scaling. The loop-based delay continues to
use loops_per_jiffy directly, as it should.
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
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When udelay() is implemented using an architected timer, it is wrong
to scale loops_per_jiffy when changing the CPU clock frequency since
the timer clock remains constant.
The lpj should probably become an implementation detail relevant to
the CPU loop based delay routine only and more confined to it. In the
mean time this is the minimal fix needed to have expected delays with
the timer based implementation when cpufreq is also in use.
Reported-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Tested-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Liviu Dudau <Liviu.Dudau@arm.com>
Cc: stable@vger.kernel.org
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
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The current timer-based delay loop relies on the architected timer to
initiate the switch away from the polling-based implementation. This is
unfortunate for platforms without the architected timers but with a
suitable delay source (that is, constant frequency, always powered-up
and ticking as long as the CPUs are online).
This patch introduces a registration mechanism for the delay timer
(which provides an unconditional read_current_timer implementation) and
updates the architected timer code to use the new interface.
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Jonathan Austin <jonathan.austin@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
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This patch allows a timer-based delay implementation to be selected by
switching the delay routines over to use get_cycles, which is
implemented in terms of read_current_timer. This further allows us to
skip the loop calibration and have a consistent delay function in the
face of core frequency scaling.
To avoid the pain of dealing with memory-mapped counters, this
implementation uses the co-processor interface to the architected timers
when they are available. The previous loop-based implementation is
kept around for CPUs without the architected timers and we retain both
the maximum delay (2ms) and the corresponding conversion factors for
determining the number of loops required for a given interval. Since the
indirection of the timer routines will only work when called from C,
the sa1100 sleep routines are modified to branch to the loop-based delay
functions directly.
Tested-by: Shinya Kuribayashi <shinya.kuribayashi.px@renesas.com>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
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Move platform independent header files to arch/arm/include/asm, leaving
those in asm/arch* and asm/plat* alone.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
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