[patch 19/46] Mark TSC on GeodeLX reliable

Thomas Gleixner
2007-01-23T22:07:08Z

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From: Marcelo Tosatti <marcelo@kvack.org>

>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 <marcelo@kvack.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

---

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 */

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