linux/arch
Maciej W. Rozycki 8533966a6d MIPS: DECstation HRT calibration bug fixes
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>
2013-09-05 20:38:28 +02:00
..
alpha alpha: Use handle_percpu_irq for the timer interrupt 2013-07-19 13:54:26 -07:00
arc ARC: [lib] strchr breakage in Big-endian configuration 2013-08-24 11:24:53 -07:00
arm Merge branch 'fixes' of git://git.linaro.org/people/rmk/linux-arm 2013-08-25 12:41:37 -07:00
arm64 Perf backend fixes for arm64 where the user can cause kernel panic 2013-08-21 16:36:32 -07:00
avr32 avr32: boards/atngw100/mrmt.c: fix building error 2013-08-08 14:16:22 +02:00
blackfin Merge branch 'cpuinit_phase2' of git://git.kernel.org/pub/scm/linux/kernel/git/paulg/linux 2013-07-18 10:50:26 -07:00
c6x Merge branch 'akpm' (updates from Andrew Morton) 2013-07-03 17:12:13 -07:00
cris cris: delete __cpuinit usage from all cris files 2013-07-14 19:36:54 -04:00
frv frv: delete __cpuinit usage from all frv files 2013-07-14 19:36:55 -04:00
h8300 net: rename busy poll socket op and globals 2013-07-10 17:08:27 -07:00
hexagon arch: *: Kconfig: add "kernel/Kconfig.freezer" to "arch/*/Kconfig" 2013-08-13 17:57:49 -07:00
ia64 Fix TLB gather virtual address range invalidation corner cases 2013-08-16 08:52:46 -07:00
m32r m32r: delete __cpuinit usage from all m32r files 2013-07-14 19:36:55 -04:00
m68k m68k: Truncate base in do_div() 2013-08-14 11:46:30 +02:00
metag metag: delete __cpuinit usage from all metag files 2013-07-14 19:36:54 -04:00
microblaze microblaze: fix clone syscall 2013-08-13 17:57:48 -07:00
mips MIPS: DECstation HRT calibration bug fixes 2013-09-05 20:38:28 +02:00
mn10300 net: rename busy poll socket op and globals 2013-07-10 17:08:27 -07:00
openrisc arch: *: Kconfig: add "kernel/Kconfig.freezer" to "arch/*/Kconfig" 2013-08-13 17:57:49 -07:00
parisc parisc: Fix interrupt routing for C8000 serial ports 2013-07-31 23:42:32 +02:00
powerpc powerpc/tm: Fix context switching TAR, PPR and DSCR SPRs 2013-08-09 18:07:12 +10:00
s390 s390: Fix broken build 2013-08-16 21:16:37 -07:00
score arch: *: Kconfig: add "kernel/Kconfig.freezer" to "arch/*/Kconfig" 2013-08-13 17:57:49 -07:00
sh Fix TLB gather virtual address range invalidation corner cases 2013-08-16 08:52:46 -07:00
sparc sparc: delete __cpuinit/__CPUINIT usage from all users 2013-07-14 19:36:52 -04:00
tile tile: delete __cpuinit usage from all tile files 2013-07-14 19:36:54 -04:00
um Fix TLB gather virtual address range invalidation corner cases 2013-08-16 08:52:46 -07:00
unicore32 reboot: move arch/x86 reboot= handling to generic kernel 2013-07-09 10:33:29 -07:00
x86 x86 get_unmapped_area: Access mmap_legacy_base through mm_struct member 2013-08-22 10:19:35 -07:00
xtensa xtensa: delete __cpuinit usage from all xtensa files 2013-07-14 19:36:56 -04:00
.gitignore
Kconfig microblaze: fix clone syscall 2013-08-13 17:57:48 -07:00