x86, lapic-timer: Increase the max_delta to 31 bits

Latest atom socs(penwell) does not have hpet timer.

As their local APIC timer is clocked at 400KHZ, and the current
code limit their Initial Counter register to 23 bits, they
cannot sleep more than 1.34 seconds which leads to ~2 spurious
wakeup per second (1 per thread)

These SOCs support 32bit timer so we change the max_delta to at
least 31bits. So we can at least sleep for 300 seconds.

We could not find any previous chip errata where lapic would
only have 23 bit precision As powertop is suggesting to activate
HPET to "sleep longer", this could mean this problem is already
known.

Problem is here since very first implementation of lapic timer
as a clock event e9e2cdb [PATCH] clockevents: i386 drivers.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Pierre Tardy <pierre.tardy@intel.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Adrian Bunk <bunk@stusta.de>
Cc: H. Peter Anvin <hpa@linux.intel.com>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Cc: Andi Kleen <ak@suse.de>
LKML-Reference: <1294327409-19426-1-git-send-email-pierre.tardy@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

authored by Pierre Tardy and committed by Ingo Molnar 4aed89d6 9adcc4a1

+1 -1
+1 -1
arch/x86/kernel/apic/apic.c
··· 684 684 lapic_clockevent.mult = div_sc(delta, TICK_NSEC * LAPIC_CAL_LOOPS, 685 685 lapic_clockevent.shift); 686 686 lapic_clockevent.max_delta_ns = 687 - clockevent_delta2ns(0x7FFFFF, &lapic_clockevent); 687 + clockevent_delta2ns(0x7FFFFFFF, &lapic_clockevent); 688 688 lapic_clockevent.min_delta_ns = 689 689 clockevent_delta2ns(0xF, &lapic_clockevent); 690 690