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>

2 files changed, 12 insertions, 0 deletions

diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt
index fc505c1b4762..f1b0eb02aa1d 100644
--- a/Documentation/feature-removal-schedule.txt
+++ b/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
 
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index c39576cb3018..525514cf33c3 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/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;
 }