x86: c1e_idle: don't mark TSC unstable if CPU has invariant TSC

Impact: Functional TSC is marked unstable on AMD family 0x10 and 0x11 CPUs.

This would be wrong because for those CPUs "invariant TSC" means:

   "The TSC counts at the same rate in all P-states, all C states, S0,
   or S1"

(See "Processor BIOS and Kernel Developer's Guides" for those CPUs.)

[ tglx: Changed C1E to AMD C1E in the printks to avoid confusion 
	with Intel C1E ]
Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/process.c

@@ -270,8 +270,9 @@ static void c1e_idle(void)
 		rdmsr(MSR_K8_INT_PENDING_MSG, lo, hi);
 		if (lo & K8_INTP_C1E_ACTIVE_MASK) {
 			c1e_detected = 1;
-			mark_tsc_unstable("TSC halt in C1E");
-			printk(KERN_INFO "System has C1E enabled\n");
+			if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
+				mark_tsc_unstable("TSC halt in AMD C1E");
+			printk(KERN_INFO "System has AMD C1E enabled\n");
 			set_cpu_cap(&boot_cpu_data, X86_FEATURE_AMDC1E);
 		}
 	}