[IA64] Fix CONFIG_PRINTK_TIME

There were two problems with enabling the PRINTK_TIME config
option:
1) The first calls to printk() occur before per-cpu data virtual
address is pinned into the TLB, so sched_clock() can fault.
2) sched_clock() is based on ar.itc, which may not be synchronized
across cpus.

Ken Chen started this patch, Tony Luck tinkered with it, and Jes
Sorensen perfected it.

Signed-off-by: Tony Luck <[e-mail]>

arch/ia64/kernel/head.S

···
 	mov ar.rsc=0		// place RSE in enforced lazy mode
 	;;
 	loadrs			// clear the dirty partition
+	mov IA64_KR(PER_CPU_DATA)=r0	// clear physical per-CPU base
 	;;
 	mov ar.bspstore=r2	// establish the new RSE stack
 	;;

arch/ia64/kernel/setup.c

···
 EXPORT_SYMBOL(__per_cpu_offset);
 #endif
 
+extern void ia64_setup_printk_clock(void);
+
 DEFINE_PER_CPU(struct cpuinfo_ia64, cpu_info);
 DEFINE_PER_CPU(unsigned long, local_per_cpu_offset);
 DEFINE_PER_CPU(unsigned long, ia64_phys_stacked_size_p8);
···
 
 	/* process SAL system table: */
 	ia64_sal_init(efi.sal_systab);
+
+	ia64_setup_printk_clock();
 
 #ifdef CONFIG_SMP
 	cpu_physical_id(0) = hard_smp_processor_id();

arch/ia64/kernel/time.c

···
 	}
 }
 EXPORT_SYMBOL(udelay);
+
+static unsigned long long ia64_itc_printk_clock(void)
+{
+	if (ia64_get_kr(IA64_KR_PER_CPU_DATA))
+		return sched_clock();
+	return 0;
+}
+
+static unsigned long long ia64_default_printk_clock(void)
+{
+	return (unsigned long long)(jiffies_64 - INITIAL_JIFFIES) *
+		(1000000000/HZ);
+}
+
+unsigned long long (*ia64_printk_clock)(void) = &ia64_default_printk_clock;
+
+unsigned long long printk_clock(void)
+{
+	return ia64_printk_clock();
+}
+
+void __init
+ia64_setup_printk_clock(void)
+{
+	if (!(sal_platform_features & IA64_SAL_PLATFORM_FEATURE_ITC_DRIFT))
+		ia64_printk_clock = ia64_itc_printk_clock;
+}

arch/ia64/sn/kernel/setup.c

···
 extern void (*ia64_mark_idle) (int);
 extern void snidle(int);
 extern unsigned char acpi_kbd_controller_present;
+extern unsigned long long (*ia64_printk_clock)(void);
 
 unsigned long sn_rtc_cycles_per_second;
 EXPORT_SYMBOL(sn_rtc_cycles_per_second);
···
 	}
 }
 
+static unsigned long sn2_rtc_initial;
+
+static unsigned long long ia64_sn2_printk_clock(void)
+{
+	unsigned long rtc_now = rtc_time();
+
+	return (rtc_now - sn2_rtc_initial) *
+		(1000000000 / sn_rtc_cycles_per_second);
+}
+
 /**
  * sn_setup - SN platform setup routine
  * @cmdline_p: kernel command line
···
 	u32 version = sn_sal_rev();
 	extern void sn_cpu_init(void);
 
+	sn2_rtc_initial = rtc_time();
 	ia64_sn_plat_set_error_handling_features();	// obsolete
 	ia64_sn_set_os_feature(OSF_MCA_SLV_TO_OS_INIT_SLV);
 	ia64_sn_set_os_feature(OSF_FEAT_LOG_SBES);
···
 	 */
 	build_cnode_tables();
 
-	/*
-	 * Old PROMs do not provide an ACPI FADT. Disable legacy keyboard
-	 * support here so we don't have to listen to failed keyboard probe
-	 * messages.
-	 */
-	if (version <= 0x0209 && acpi_kbd_controller_present) {
-		printk(KERN_INFO "Disabling legacy keyboard support as prom "
-		       "is too old and doesn't provide FADT\n");
-		acpi_kbd_controller_present = 0;
-	}
-
-	printk("SGI SAL version %x.%02x\n", version >> 8, version & 0x00FF);
-
 	status =
 	    ia64_sal_freq_base(SAL_FREQ_BASE_REALTIME_CLOCK, &ticks_per_sec,
 			       &drift);
···
 		sn_rtc_cycles_per_second = ticks_per_sec;
 
 	platform_intr_list[ACPI_INTERRUPT_CPEI] = IA64_CPE_VECTOR;
+
+	ia64_printk_clock = ia64_sn2_printk_clock;
+
+	/*
+	 * Old PROMs do not provide an ACPI FADT. Disable legacy keyboard
+	 * support here so we don't have to listen to failed keyboard probe
+	 * messages.
+	 */
+	if (version <= 0x0209 && acpi_kbd_controller_present) {
+		printk(KERN_INFO "Disabling legacy keyboard support as prom "
+		       "is too old and doesn't provide FADT\n");
+		acpi_kbd_controller_present = 0;
+	}
+
+	printk("SGI SAL version %x.%02x\n", version >> 8, version & 0x00FF);
 
 	/*
 	 * we set the default root device to /dev/hda