[PATCH] Mark TSC on GeodeLX reliable
Marcelo Tosatti [Fri, 16 Feb 2007 09:27:44 +0000 (01:27 -0800)]
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>

arch/i386/kernel/tsc.c
include/asm-i386/msr.h

index 22931d2..3082a41 100644 (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);
index 609a389..6db40d0 100644 (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 */