Not all I/O ASIC versions have the free-running counter implemented, an
early revision used in the 5000/1xx models aka 3MIN and 4MIN did not have
it. Therefore we cannot unconditionally use it as a clock source.
Fortunately if not implemented its register slot has a fixed value so it
is enough if we check for the value at the end of the calibration period
being the same as at the beginning.
This also means we need to look for another high-precision clock source on
the systems affected. The 5000/1xx can have an R4000SC processor
installed where the CP0 Count register can be used as a clock source.
Unfortunately all the R4k DECstations suffer from the missed timer
interrupt on CP0 Count reads erratum, so we cannot use the CP0 timer as a
clock source and a clock event both at a time. However we never need an
R4k clock event device because all DECstations have a DS1287A RTC chip
whose periodic interrupt can be used as a clock source.
This gives us the following four configuration possibilities for I/O ASIC
DECstations:
1. No I/O ASIC counter and no CP0 timer, e.g. R3k 5000/1xx (3MIN).
2. No I/O ASIC counter but the CP0 timer, i.e. R4k 5000/150 (4MIN).
3. The I/O ASIC counter but no CP0 timer, e.g. R3k 5000/240 (3MAX+).
4. The I/O ASIC counter and the CP0 timer, e.g. R4k 5000/260 (4MAX+).
For #1 and #2 this change stops the I/O ASIC free-running counter from
being installed as a clock source of a 0Hz frequency. For #2 it also
arranges for the CP0 timer to be used as a clock source rather than a
clock event device, because having an accurate wall clock is more
important than a high-precision interval timer. For #3 there is no
change. For #4 the change makes the I/O ASIC free-running counter
installed as a clock source so that the CP0 timer can be used as a clock
event device.
Unfortunately the use of the CP0 timer as a clock event device relies on a
succesful completion of c0_compare_interrupt. That never happens, because
while waiting for a CP0 Compare interrupt to happen the function spins in
a loop reading the CP0 Count register. This makes the CP0 Count erratum
trigger reliably causing the interrupt waited for to be lost in all cases.
As a result #4 resorts to using the CP0 timer as a clock source as well,
just as #2. However we want to keep this separate arrangement in case
(hope) c0_compare_interrupt is eventually rewritten such that it avoids
the erratum.
Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/5825/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
This change corrects DECstation HRT calibration, by removing the following
bugs:
1. Calibration period selection -- HZ / 10 has been chosen, however on
DECstation computers, HZ never divides by 10, as the choice for HZ is
among 128, 256 and 1024. The choice therefore results in a systematic
calibration error, e.g. 6.25% for the usual choice of 128 for HZ:
128 / 10 * 10 = 120
(128 - 120) / 128 -> 6.25%
The change therefore makes calibration use HZ / 8 that is always
accurate for the HZ values available, getting rid of the systematic
error.
2. Calibration starting point synchronisation -- the duration of a number
of intervals between DS1287A periodic interrupt assertions is measured,
however code does not ensure at the beginning that the interrupt has
not been previously asserted. This results in a variable error of e.g.
up to another 6.25% for the period of HZ / 8 (8.(3)% with the original
HZ / 10 period) and the usual choice of 128 for HZ:
1 / 16 -> 6.25%
1 / 12 -> 8.(3)%
The change therefore adds an initial call to ds1287_timer_state that
clears any previous periodic interrupt pending.
The same issue applies to both I/O ASIC counter and R4k CP0 timer
calibration on DECstation systems as similar code is used in both cases
and both pieces of code are covered by this fix.
On an R3400 test system used this fix results in a change of the I/O ASIC
clock frequency reported from values like:
I/O ASIC clock frequency 23185830Hz
to:
I/O ASIC clock frequency 24999288Hz
removing the miscalculation by 6.25% from the systematic error and (for
the individual sample provided) a further 1.00% from the variable error,
accordingly. The nominal I/O ASIC clock frequency is 25MHz on this
system.
Here's another result, with the fix applied, from a system that has both
HRTs available (using an R4400 at 60MHz nominal):
MIPS counter frequency 59999328Hz
I/O ASIC clock frequency 24999432Hz
Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/5807/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Having received another series of whitespace patches I decided to do this
once and for all rather than dealing with this kind of patches trickling
in forever.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
This converts the mips clocksources to use clocksource_register_hz/khz
CC: Ralf Baechle <ralf@linux-mips.org>
CC: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Pass clocksource pointer to the read() callback for clocksources. This
allows us to share the callback between multiple instances.
[hugh@veritas.com: fix powerpc build of clocksource pass clocksource mods]
[akpm@linux-foundation.org: cleanup]
Signed-off-by: Magnus Damm <damm@igel.co.jp>
Acked-by: John Stultz <johnstul@us.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
