[Xen-devel] [PATCH 1/4] mwait-idle: allow sparse sub-state numbering, for Bay Trail

["Jan Beulich" <JBeulich@xxxxxxxx>]

From: Len Brown <len.brown@xxxxxxxxx>

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@xxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/cpu/mwait-idle.c
+++ b/xen/arch/x86/cpu/mwait-idle.c
@@ -557,23 +557,22 @@ static int mwait_idle_cpu_init(struct no
        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) {

Attachment: x86-mwait-sparse-substates.patch
Description: Text document

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