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[PATCH] Mark TSC on GeodeLX reliable

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The Geode can safely use the TSC for highres, since:

1) Does not support frequency scaling,

2) The TSC _does_ count when the CPU is halted.  Furthermore, the Geode
   supports a mode called "suspension on halt", where Suspend mode (which
   interacts with the power management states) is entered.  TSC counting
   during suspend mode is controlled by bit 8 of the Bus Controller
   Configuration Register #0 (thanks Tom!).

3) no SMP :)

Check if "RTSC counts during suspension" and remove the requirement for
verification, so the clocksource code can safely select it as an timesource
for the highres timers subsystem.

Signed-off-by: Marcelo Tosatti <marcelo@kvack.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Marcelo Tosatti 2007-02-16 01:27:44 -08:00 committed by Linus Torvalds
parent 5d8b34fdcb
commit 07190a08ee
2 changed files with 23 additions and 0 deletions
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20
arch/i386/kernel/tsc.c
View File

@ -364,6 +364,25 @@ __cpuinit int unsynchronized_tsc(void)
return tsc_unstable;
}
/*
* Geode_LX - the OLPC CPU has a possibly a very reliable TSC
*/
#ifdef CONFIG_MGEODE_LX
/* RTSC counts during suspend */
#define RTSC_SUSP 0x100
static void __init check_geode_tsc_reliable(void)
{
unsigned long val;
rdmsrl(MSR_GEODE_BUSCONT_CONF0, val);
if ((val & RTSC_SUSP))
clocksource_tsc.flags &= ~CLOCK_SOURCE_MUST_VERIFY;
}
#else
static inline void check_geode_tsc_reliable(void) { }
#endif
static int __init init_tsc_clocksource(void)
{
@ -372,6 +391,7 @@ static int __init init_tsc_clocksource(void)
dmi_check_system(bad_tsc_dmi_table);
unsynchronized_tsc();
check_geode_tsc_reliable();
current_tsc_khz = tsc_khz;
clocksource_tsc.mult = clocksource_khz2mult(current_tsc_khz,
clocksource_tsc.shift);

3
include/asm-i386/msr.h
View File

@ -307,4 +307,7 @@ static inline void wrmsrl (unsigned long msr, unsigned long long val)
#define MSR_CORE_PERF_GLOBAL_CTRL 0x38f
#define MSR_CORE_PERF_GLOBAL_OVF_CTRL 0x390
/* Geode defined MSRs */
#define MSR_GEODE_BUSCONT_CONF0 0x1900
#endif /* __ASM_MSR_H */