mwait-idle: allow sparse sub-state numbering, for Bay Trail

Like acpi_idle, mwait-idle compared sub-state numbers
to the number of supported sub-states -- discarding
sub-states numbers that were numbered >= the number of states.

But some Bay Trail SOCs use sparse sub-state numbers,
so we can't make such a comparison if we are going
to access those states.

So now we simply check that _some_ sub-states are
supported for the given state, and assume that the
sub-state number in our driver is valid.

In practice, the driver is correct, and even if it were not,
the hardware clips invalid sub-state requests to valid ones.

No entries in the driver require this change,
but Bay Trail will need it.

Signed-off-by: Len Brown <len.brown@intel.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/cpu/mwait-idle.c

@@ -555,23 +555,22 @@ static int mwait_idle_cpu_init(struct notifier_block *nfb,
 	dev->count = 1;
 
 	for (cstate = 0; cpuidle_state_table[cstate].target_residency; ++cstate) {
-		unsigned int num_substates, hint, state, substate;
+		unsigned int num_substates, hint, state;
 		struct acpi_processor_cx *cx;
 
 		hint = flg2MWAIT(cpuidle_state_table[cstate].flags);
 		state = MWAIT_HINT2CSTATE(hint) + 1;
-		substate = MWAIT_HINT2SUBSTATE(hint);
 
 		if (state > max_cstate) {
 			printk(PREFIX "max C-state %u reached\n", max_cstate);
 			break;
 		}
 
-		/* Does the state exist in CPUID.MWAIT? */
+		/* Number of sub-states for this state in CPUID.MWAIT. */
 		num_substates = (mwait_substates >> (state * 4))
 		                & MWAIT_SUBSTATE_MASK;
-		/* if sub-state in table is not enumerated by CPUID */
-		if (substate >= num_substates)
+		/* If NO sub-states for this state in CPUID, skip it. */
+		if (num_substates == 0)
 			continue;
 
 		if (dev->count >= ACPI_PROCESSOR_MAX_POWER) {