ACPI: Enable C3 even when PM2_control is zero

On systems that do not have pm2_control_block, we cannot really use
ARB_DISABLE before C3. We used to disable C3 totally on such systems.

To be compatible with Windows, we need to enable C3 on such systems now.
We just skip ARB_DISABLE step before entering the C3-state and assume
hardware is handling things correctly. Also, ACPI spec is not clear
about pm2_control is _needed_ for C3 or not.

We have atleast one system that need this to enable C3.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>

diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index ee5759bef9454df682d7520032e8c33f5bfbc0b8..36dc1d26520a0b8969528668bd74720dc391a0ad 100644 (file)
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -488,7 +488,17 @@ static void acpi_processor_idle(void)
 
        case ACPI_STATE_C3:
 
-               if (pr->flags.bm_check) {
+               /*
+                * disable bus master
+                * bm_check implies we need ARB_DIS
+                * !bm_check implies we need cache flush
+                * bm_control implies whether we can do ARB_DIS
+                *
+                * That leaves a case where bm_check is set and bm_control is
+                * not set. In that case we cannot do much, we enter C3
+                * without doing anything.
+                */
+               if (pr->flags.bm_check && pr->flags.bm_control) {
                        if (atomic_inc_return(&c3_cpu_count) ==
                            num_online_cpus()) {
                                /*
@@ -497,7 +507,7 @@ static void acpi_processor_idle(void)
                                 */
                                acpi_set_register(ACPI_BITREG_ARB_DISABLE, 1);
                        }
-               } else {
+               } else if (!pr->flags.bm_check) {
                        /* SMP with no shared cache... Invalidate cache  */
                        ACPI_FLUSH_CPU_CACHE();
                }
@@ -509,7 +519,7 @@ static void acpi_processor_idle(void)
                acpi_cstate_enter(cx);
                /* Get end time (ticks) */
                t2 = inl(acpi_gbl_FADT.xpm_timer_block.address);
-               if (pr->flags.bm_check) {
+               if (pr->flags.bm_check && pr->flags.bm_control) {
                        /* Enable bus master arbitration */
                        atomic_dec(&c3_cpu_count);
                        acpi_set_register(ACPI_BITREG_ARB_DISABLE, 0);
@@ -959,9 +969,9 @@ static void acpi_processor_power_verify_c3(struct acpi_processor *pr,
        if (pr->flags.bm_check) {
                /* bus mastering control is necessary */
                if (!pr->flags.bm_control) {
+                       /* In this case we enter C3 without bus mastering */
                        ACPI_DEBUG_PRINT((ACPI_DB_INFO,
-                                         "C3 support requires bus mastering control\n"));
-                       return;
+                               "C3 support without bus mastering control\n"));
                }
        } else {
                /*