[PATCH] x86_64: Auto enable HPET on Summit

From: James Cleverdon

Switch to HPET timer automatically mode on Summit 2
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/x86_64/kernel/apic.c

@@ -905,6 +905,54 @@ void smp_apic_timer_interrupt(struct pt_regs *regs)
 	irq_exit();
 }
 
+/*
+ * oem_force_hpet_timer -- force HPET mode for some boxes.
+ *
+ * Thus far, the major user of this is IBM's Summit2 series:
+ *
+ * Clustered boxes may have unsynced TSC problems if they are
+ * multi-chassis. Use available data to take a good guess.
+ * If in doubt, go HPET.
+ */
+__init int oem_force_hpet_timer(void)
+{
+	int i, clusters, zeros;
+	unsigned id;
+	DECLARE_BITMAP(clustermap, NUM_APIC_CLUSTERS);
+
+	bitmap_empty(clustermap, NUM_APIC_CLUSTERS);
+
+	for (i = 0; i < NR_CPUS; i++) {
+		id = bios_cpu_apicid[i];
+		if (id != BAD_APICID)
+			__set_bit(APIC_CLUSTERID(id), clustermap);
+	}
+
+	/* Problem:  Partially populated chassis may not have CPUs in some of
+	 * the APIC clusters they have been allocated.  Only present CPUs have
+	 * bios_cpu_apicid entries, thus causing zeroes in the bitmap.  Since
+	 * clusters are allocated sequentially, count zeros only if they are
+	 * bounded by ones.
+	 */
+	clusters = 0;
+	zeros = 0;
+	for (i = 0; i < NUM_APIC_CLUSTERS; i++) {
+		if (test_bit(i, clustermap)) {
+			clusters += 1 + zeros;
+			zeros = 0;
+		} else
+			++zeros;
+	}
+
+	/*
+	 * If clusters > 2, then should be multi-chassis.  Return 1 for HPET.
+	 * Else return 0 to use TSC.
+	 * May have to revisit this when multi-core + hyperthreaded CPUs come
+	 * out, but AFAIK this will work even for them.
+	 */
+	return (clusters > 2);
+}
+
 /*
  * This interrupt should _never_ happen with our APIC/SMP architecture
  */

arch/x86_64/kernel/time.c

@@ -928,7 +928,7 @@ void __init time_init_smp(void)
 	 * the TSC.
 	 *
 	 * Exceptions:
-	 * IBM Summit. Will need to be special cased later.
+	 * IBM Summit2 checked by oem_force_hpet_timer().
  	 * AMD dual core may also not need HPET. Check me.
 	 *
 	 * Can be turned off with "notsc".
@@ -936,6 +936,9 @@ void __init time_init_smp(void)
 	if (num_online_cpus() > 1 &&
 	    boot_cpu_data.x86_vendor == X86_VENDOR_AMD)
 		notsc = 1;
+	/* Some systems will want to disable TSC and use HPET. */
+	if (oem_force_hpet_timer())
+		notsc = 1;
 	if (vxtime.hpet_address && notsc) {
 		timetype = "HPET";
 		vxtime.last = hpet_readl(HPET_T0_CMP) - hpet_tick;

include/asm-x86_64/hpet.h

@@ -54,6 +54,7 @@ extern int hpet_set_alarm_time(unsigned char hrs, unsigned char min, unsigned ch
 extern int hpet_set_periodic_freq(unsigned long freq);
 extern int hpet_rtc_dropped_irq(void);
 extern int hpet_rtc_timer_init(void);
+extern int oem_force_hpet_timer(void);
 #endif /* CONFIG_HPET_EMULATE_RTC */
 
 #endif