[PATCH] Make sched_clock() work in early boot

[Jason Uhlenkott <jasonuhl@sgi.com>]

Turning on PRINTK_TIME causes us to die in early boot when sched_clock()
tries to access per-cpu data which isn't set up yet.

We can avoid this by doing a speculative load on the per-cpu data and
just returning zero if we fail.  This matches the way sched_clock()
appears to behave on most other arches if it gets called before we
know the cpu frequency.

Signed-off-by: Jason Uhlenkott <jasonuhl@sgi.com>

Index: linux/arch/ia64/kernel/head.S
=================================--- linux.orig/arch/ia64/kernel/head.S	2005-08-15 15:54:56.130313231 -0700
+++ linux/arch/ia64/kernel/head.S	2005-08-16 12:49:23.843747550 -0700
@@ -983,9 +983,10 @@
 	addl r8=THIS_CPU(cpu_info) + IA64_CPUINFO_NSEC_PER_CYC_OFFSET,r0
 	mov.m r9=ar.itc		// fetch cycle-counter				(35 cyc)
 	;;
-	ldf8 f8=[r8]
+	ldf8.s f8=[r8]
 	;;
 	setf.sig f9=r9		// certain to stall, so issue it _after_ ldf8...
+	chk.s r8, .recover
 	;;
 	xmpy.lu f10ù,f8	// calculate low 64 bits of 128-bit product	(4 cyc)
 	xmpy.hu f11ù,f8	// calculate high 64 bits of 128-bit product
@@ -995,6 +996,10 @@
 	;;
 	shrp r8=r9,r8,IA64_NSEC_PER_CYC_SHIFT
 	br.ret.sptk.many rp
+.recover:			// per-cpu data isn't set up yet,
+				// so just return 0.
+	mov r8=r0
+	br.ret.sptk.many rp
 END(sched_clock)
 
 GLOBAL_ENTRY(start_kernel_thread)