From: Marcelo Tosatti >>From what I can tell 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 Signed-off-by: Thomas Gleixner Signed-off-by: Ingo Molnar --- arch/i386/kernel/tsc.c | 20 ++++++++++++++++++++ include/asm-i386/msr.h | 3 +++ 2 files changed, 23 insertions(+) Index: linux-2.6.20-rc4-mm1-bo/arch/i386/kernel/tsc.c =================================================================== --- linux-2.6.20-rc4-mm1-bo.orig/arch/i386/kernel/tsc.c +++ linux-2.6.20-rc4-mm1-bo/arch/i386/kernel/tsc.c @@ -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(v 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); Index: linux-2.6.20-rc4-mm1-bo/include/asm-i386/msr.h =================================================================== --- linux-2.6.20-rc4-mm1-bo.orig/include/asm-i386/msr.h +++ linux-2.6.20-rc4-mm1-bo/include/asm-i386/msr.h @@ -307,4 +307,7 @@ static inline void wrmsrl (unsigned long #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 */ -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/