x86 idle: deprecate "no-hlt" cmdline param

We'd rather that modern machines not check if HLT works on
every entry into idle, for the benefit of machines that had
marginal electricals 15-years ago.  If those machines are still running
the upstream kernel, they can use "idle=poll".  The only difference
will be that they'll now invoke HLT in machine_hlt().

cc: x86@kernel.org # .39.x
Signed-off-by: Len Brown <len.brown@intel.com>

Documentation/feature-removal-schedule.txt

@@ -24,6 +24,17 @@ Who:	Len Brown <len.brown@intel.com>
 
 ----------------------------
 
+What:	x86_32 "no-hlt" cmdline param
+When:	2012
+Why:	remove a branch from idle path, simplify code used by everybody.
+	This option disabled the use of HLT in idle and machine_halt()
+	for hardware that was flakey 15-years ago.  Today we have
+	"idle=poll" that removed HLT from idle, and so if such a machine
+	is still running the upstream kernel, "idle=poll" is likely sufficient.
+Who:	Len Brown <len.brown@intel.com>
+
+----------------------------
+
 What:	PRISM54
 When:	2.6.34
 

arch/x86/kernel/cpu/bugs.c

@@ -19,6 +19,7 @@
 
 static int __init no_halt(char *s)
 {
+	WARN_ONCE(1, "\"no-hlt\" is deprecated, please use \"idle=poll\"\n");
 	boot_cpu_data.hlt_works_ok = 0;
 	return 1;
 }