ACPI: Processor native C-states using MWAIT

Intel processors starting with the Core Duo support
support processor native C-state using the MWAIT instruction.
Refer: Intel Architecture Software Developer's Manual
http://www.intel.com/design/Pentium4/manuals/253668.htm

Platform firmware exports the support for Native C-state to OS using
ACPI _PDC and _CST methods.
Refer: Intel Processor Vendor-Specific ACPI: Interface Specification
http://www.intel.com/technology/iapc/acpi/downloads/302223.htm

With Processor Native C-state, we use 'MWAIT' instruction on the processor
to enter different C-states (C1, C2, C3). We won't use the special IO
ports to enter C-state and no SMM mode etc required to enter C-state.
Overall this will mean better C-state support.

One major advantage of using MWAIT for all C-states is, with this and
"treat interrupt as break event" feature of MWAIT, we can now get accurate
timing for the time spent in C1, C2, .. states.

Signed-off-by: Venkatesh Pallipadi <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Len Brown <[e-mail]>

arch/i386/kernel/acpi/cstate.c

···
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/acpi.h>
+#include <linux/cpu.h>
 
 #include <acpi/processor.h>
 #include <asm/acpi.h>
···
 		flags->bm_check = 1;
 	}
 }
-
 EXPORT_SYMBOL(acpi_processor_power_init_bm_check);
+
+/* The code below handles cstate entry with monitor-mwait pair on Intel*/
+
+struct cstate_entry_s {
+	struct {
+		unsigned int eax;
+		unsigned int ecx;
+	} states[ACPI_PROCESSOR_MAX_POWER];
+};
+static struct cstate_entry_s *cpu_cstate_entry;	/* per CPU ptr */
+
+static short mwait_supported[ACPI_PROCESSOR_MAX_POWER];
+
+#define MWAIT_SUBSTATE_MASK	(0xf)
+#define MWAIT_SUBSTATE_SIZE	(4)
+
+#define CPUID_MWAIT_LEAF (5)
+#define CPUID5_ECX_EXTENSIONS_SUPPORTED (0x1)
+#define CPUID5_ECX_INTERRUPT_BREAK	(0x2)
+
+#define MWAIT_ECX_INTERRUPT_BREAK	(0x1)
+
+#define NATIVE_CSTATE_BEYOND_HALT	(2)
+
+int acpi_processor_ffh_cstate_probe(unsigned int cpu,
+		struct acpi_processor_cx *cx, struct acpi_power_register *reg)
+{
+	struct cstate_entry_s *percpu_entry;
+	struct cpuinfo_x86 *c = cpu_data + cpu;
+
+	cpumask_t saved_mask;
+	int retval;
+	unsigned int eax, ebx, ecx, edx;
+	unsigned int edx_part;
+	unsigned int cstate_type; /* C-state type and not ACPI C-state type */
+	unsigned int num_cstate_subtype;
+
+	if (!cpu_cstate_entry || c->cpuid_level < CPUID_MWAIT_LEAF )
+		return -1;
+
+	if (reg->bit_offset != NATIVE_CSTATE_BEYOND_HALT)
+		return -1;
+
+	percpu_entry = per_cpu_ptr(cpu_cstate_entry, cpu);
+	percpu_entry->states[cx->index].eax = 0;
+	percpu_entry->states[cx->index].ecx = 0;
+
+	/* Make sure we are running on right CPU */
+	saved_mask = current->cpus_allowed;
+	retval = set_cpus_allowed(current, cpumask_of_cpu(cpu));
+	if (retval)
+		return -1;
+
+	cpuid(CPUID_MWAIT_LEAF, &eax, &ebx, &ecx, &edx);
+
+	/* Check whether this particular cx_type (in CST) is supported or not */
+	cstate_type = (cx->address >> MWAIT_SUBSTATE_SIZE) + 1;
+	edx_part = edx >> (cstate_type * MWAIT_SUBSTATE_SIZE);
+	num_cstate_subtype = edx_part & MWAIT_SUBSTATE_MASK;
+
+	retval = 0;
+	if (num_cstate_subtype < (cx->address & MWAIT_SUBSTATE_MASK)) {
+		retval = -1;
+		goto out;
+	}
+
+	/* mwait ecx extensions INTERRUPT_BREAK should be supported for C2/C3 */
+	if (!(ecx & CPUID5_ECX_EXTENSIONS_SUPPORTED) ||
+	    !(ecx & CPUID5_ECX_INTERRUPT_BREAK)) {
+		retval = -1;
+		goto out;
+	}
+	percpu_entry->states[cx->index].ecx = MWAIT_ECX_INTERRUPT_BREAK;
+
+	/* Use the hint in CST */
+	percpu_entry->states[cx->index].eax = cx->address;
+
+	if (!mwait_supported[cstate_type]) {
+		mwait_supported[cstate_type] = 1;
+		printk(KERN_DEBUG "Monitor-Mwait will be used to enter C-%d "
+		       "state\n", cx->type);
+	}
+
+out:
+	set_cpus_allowed(current, saved_mask);
+	return retval;
+}
+EXPORT_SYMBOL_GPL(acpi_processor_ffh_cstate_probe);
+
+void acpi_processor_ffh_cstate_enter(struct acpi_processor_cx *cx)
+{
+	unsigned int cpu = smp_processor_id();
+	struct cstate_entry_s *percpu_entry;
+
+	percpu_entry = per_cpu_ptr(cpu_cstate_entry, cpu);
+	mwait_idle_with_hints(percpu_entry->states[cx->index].eax,
+	                      percpu_entry->states[cx->index].ecx);
+}
+EXPORT_SYMBOL_GPL(acpi_processor_ffh_cstate_enter);
+
+static int __init ffh_cstate_init(void)
+{
+	struct cpuinfo_x86 *c = &boot_cpu_data;
+	if (c->x86_vendor != X86_VENDOR_INTEL)
+		return -1;
+
+	cpu_cstate_entry = alloc_percpu(struct cstate_entry_s);
+	return 0;
+}
+
+static void __exit ffh_cstate_exit(void)
+{
+	if (cpu_cstate_entry) {
+		free_percpu(cpu_cstate_entry);
+		cpu_cstate_entry = NULL;
+	}
+}
+
+arch_initcall(ffh_cstate_init);
+__exitcall(ffh_cstate_exit);

arch/i386/kernel/process.c

···
  * We execute MONITOR against need_resched and enter optimized wait state
  * through MWAIT. Whenever someone changes need_resched, we would be woken
  * up from MWAIT (without an IPI).
+ *
+ * New with Core Duo processors, MWAIT can take some hints based on CPU
+ * capability.
  */
+void mwait_idle_with_hints(unsigned long eax, unsigned long ecx)
+{
+	if (!need_resched()) {
+		__monitor((void *)&current_thread_info()->flags, 0, 0);
+		smp_mb();
+		if (!need_resched())
+			__mwait(eax, ecx);
+	}
+}
+
+/* Default MONITOR/MWAIT with no hints, used for default C1 state */
 static void mwait_idle(void)
 {
 	local_irq_enable();
-
-	while (!need_resched()) {
-		__monitor((void *)&current_thread_info()->flags, 0, 0);
-		smp_mb();
-		if (need_resched())
-			break;
-		__mwait(0, 0);
-	}
+	while (!need_resched())
+		mwait_idle_with_hints(0, 0);
 }
 
 void __devinit select_idle_routine(const struct cpuinfo_x86 *c)

arch/x86_64/kernel/process.c

···
  * We execute MONITOR against need_resched and enter optimized wait state
  * through MWAIT. Whenever someone changes need_resched, we would be woken
  * up from MWAIT (without an IPI).
+ *
+ * New with Core Duo processors, MWAIT can take some hints based on CPU
+ * capability.
  */
+void mwait_idle_with_hints(unsigned long eax, unsigned long ecx)
+{
+	if (!need_resched()) {
+		__monitor((void *)&current_thread_info()->flags, 0, 0);
+		smp_mb();
+		if (!need_resched())
+			__mwait(eax, ecx);
+	}
+}
+
+/* Default MONITOR/MWAIT with no hints, used for default C1 state */
 static void mwait_idle(void)
 {
 	local_irq_enable();
-
-	while (!need_resched()) {
-		__monitor((void *)&current_thread_info()->flags, 0, 0);
-		smp_mb();
-		if (need_resched())
-			break;
-		__mwait(0, 0);
-	}
+	while (!need_resched())
+		mwait_idle_with_hints(0,0);
 }
 
 void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)

drivers/acpi/processor_idle.c

···
 
 static atomic_t c3_cpu_count;
 
+/* Common C-state entry for C2, C3, .. */
+static void acpi_cstate_enter(struct acpi_processor_cx *cstate)
+{
+	if (cstate->space_id == ACPI_CSTATE_FFH) {
+		/* Call into architectural FFH based C-state */
+		acpi_processor_ffh_cstate_enter(cstate);
+	} else {
+		int unused;
+		/* IO port based C-state */
+		inb(cstate->address);
+		/* Dummy wait op - must do something useless after P_LVL2 read
+		   because chipsets cannot guarantee that STPCLK# signal
+		   gets asserted in time to freeze execution properly. */
+		unused = inl(acpi_fadt.xpm_tmr_blk.address);
+	}
+}
+
 static void acpi_processor_idle(void)
 {
 	struct acpi_processor *pr = NULL;
···
 		/* Get start time (ticks) */
 		t1 = inl(acpi_fadt.xpm_tmr_blk.address);
 		/* Invoke C2 */
-		inb(cx->address);
-		/* Dummy wait op - must do something useless after P_LVL2 read
-		   because chipsets cannot guarantee that STPCLK# signal
-		   gets asserted in time to freeze execution properly. */
-		t2 = inl(acpi_fadt.xpm_tmr_blk.address);
+		acpi_cstate_enter(cx);
 		/* Get end time (ticks) */
 		t2 = inl(acpi_fadt.xpm_tmr_blk.address);
 
···
 		/* Get start time (ticks) */
 		t1 = inl(acpi_fadt.xpm_tmr_blk.address);
 		/* Invoke C3 */
-		inb(cx->address);
-		/* Dummy wait op (see above) */
-		t2 = inl(acpi_fadt.xpm_tmr_blk.address);
+		acpi_cstate_enter(cx);
 		/* Get end time (ticks) */
 		t2 = inl(acpi_fadt.xpm_tmr_blk.address);
 		if (pr->flags.bm_check) {
···
 	return 0;
 }
 
-static int acpi_processor_get_power_info_default_c1(struct acpi_processor *pr)
+static int acpi_processor_get_power_info_default(struct acpi_processor *pr)
 {
-
-	/* Zero initialize all the C-states info. */
-	memset(pr->power.states, 0, sizeof(pr->power.states));
-
-	/* set the first C-State to C1 */
-	pr->power.states[ACPI_STATE_C1].type = ACPI_STATE_C1;
-
-	/* the C0 state only exists as a filler in our array,
-	 * and all processors need to support C1 */
+	if (!pr->power.states[ACPI_STATE_C1].valid) {
+		/* set the first C-State to C1 */
+		/* all processors need to support C1 */
+		pr->power.states[ACPI_STATE_C1].type = ACPI_STATE_C1;
+		pr->power.states[ACPI_STATE_C1].valid = 1;
+	}
+	/* the C0 state only exists as a filler in our array */
 	pr->power.states[ACPI_STATE_C0].valid = 1;
-	pr->power.states[ACPI_STATE_C1].valid = 1;
-
 	return 0;
 }
 
···
 	if (nocst)
 		return -ENODEV;
 
-	current_count = 1;
-
-	/* Zero initialize C2 onwards and prepare for fresh CST lookup */
-	for (i = 2; i < ACPI_PROCESSOR_MAX_POWER; i++)
-		memset(&(pr->power.states[i]), 0, 
-				sizeof(struct acpi_processor_cx));
+	current_count = 0;
 
 	status = acpi_evaluate_object(pr->handle, "_CST", NULL, &buffer);
 	if (ACPI_FAILURE(status)) {
···
 		    (reg->space_id != ACPI_ADR_SPACE_FIXED_HARDWARE))
 			continue;
 
-		cx.address = (reg->space_id == ACPI_ADR_SPACE_FIXED_HARDWARE) ?
-		    0 : reg->address;
-
 		/* There should be an easy way to extract an integer... */
 		obj = (union acpi_object *)&(element->package.elements[1]);
 		if (obj->type != ACPI_TYPE_INTEGER)
 			continue;
 
 		cx.type = obj->integer.value;
+		/*
+		 * Some buggy BIOSes won't list C1 in _CST -
+		 * Let acpi_processor_get_power_info_default() handle them later
+		 */
+		if (i == 1 && cx.type != ACPI_STATE_C1)
+			current_count++;
 
-		if ((cx.type != ACPI_STATE_C1) &&
-		    (reg->space_id != ACPI_ADR_SPACE_SYSTEM_IO))
-			continue;
+		cx.address = reg->address;
+		cx.index = current_count + 1;
 
-		if ((cx.type < ACPI_STATE_C2) || (cx.type > ACPI_STATE_C3))
-			continue;
+		cx.space_id = ACPI_CSTATE_SYSTEMIO;
+		if (reg->space_id == ACPI_ADR_SPACE_FIXED_HARDWARE) {
+			if (acpi_processor_ffh_cstate_probe
+					(pr->id, &cx, reg) == 0) {
+				cx.space_id = ACPI_CSTATE_FFH;
+			} else if (cx.type != ACPI_STATE_C1) {
+				/*
+				 * C1 is a special case where FIXED_HARDWARE
+				 * can be handled in non-MWAIT way as well.
+				 * In that case, save this _CST entry info.
+				 * That is, we retain space_id of SYSTEM_IO for
+				 * halt based C1.
+				 * Otherwise, ignore this info and continue.
+				 */
+				continue;
+			}
+		}
 
 		obj = (union acpi_object *)&(element->package.elements[2]);
 		if (obj->type != ACPI_TYPE_INTEGER)
···
 	/* NOTE: the idle thread may not be running while calling
 	 * this function */
 
-	/* Adding C1 state */
-	acpi_processor_get_power_info_default_c1(pr);
+	/* Zero initialize all the C-states info. */
+	memset(pr->power.states, 0, sizeof(pr->power.states));
+
 	result = acpi_processor_get_power_info_cst(pr);
 	if (result == -ENODEV)
 		acpi_processor_get_power_info_fadt(pr);
+
+	if (result)
+		return result;
+
+	acpi_processor_get_power_info_default(pr);
 
 	pr->power.count = acpi_processor_power_verify(pr);
 

include/acpi/pdc_intel.h

···
 #define ACPI_PDC_SMP_C_SWCOORD		(0x0040)
 #define ACPI_PDC_SMP_T_SWCOORD		(0x0080)
 #define ACPI_PDC_C_C1_FFH		(0x0100)
+#define ACPI_PDC_C_C2C3_FFH		(0x0200)
 
 #define ACPI_PDC_EST_CAPABILITY_SMP	(ACPI_PDC_SMP_C1PT | \
 					 ACPI_PDC_C_C1_HALT | \
···
 					 ACPI_PDC_SMP_P_SWCOORD | \
 					 ACPI_PDC_P_FFH)
 
-#define ACPI_PDC_C_CAPABILITY_SMP	(ACPI_PDC_SMP_C2C3 | \
-					 ACPI_PDC_SMP_C1PT | \
-					 ACPI_PDC_C_C1_HALT)
+#define ACPI_PDC_C_CAPABILITY_SMP	(ACPI_PDC_SMP_C2C3  | \
+					 ACPI_PDC_SMP_C1PT  | \
+					 ACPI_PDC_C_C1_HALT | \
+					 ACPI_PDC_C_C1_FFH  | \
+					 ACPI_PDC_C_C2C3_FFH)
 
 #endif				/* __PDC_INTEL_H__ */

include/acpi/processor.h

···
 #define DOMAIN_COORD_TYPE_SW_ANY	0xfd
 #define DOMAIN_COORD_TYPE_HW_ALL	0xfe
 
+#define ACPI_CSTATE_SYSTEMIO	(0)
+#define ACPI_CSTATE_FFH		(1)
+
 /* Power Management */
 
 struct acpi_processor_cx;
···
 	u8 valid;
 	u8 type;
 	u32 address;
+	u8 space_id;
+	u8 index;
 	u32 latency;
 	u32 latency_ticks;
 	u32 power;
···
 #ifdef ARCH_HAS_POWER_INIT
 void acpi_processor_power_init_bm_check(struct acpi_processor_flags *flags,
 					unsigned int cpu);
+int acpi_processor_ffh_cstate_probe(unsigned int cpu,
+		struct acpi_processor_cx *cx, struct acpi_power_register *reg);
+void acpi_processor_ffh_cstate_enter(struct acpi_processor_cx *cstate);
 #else
 static inline void acpi_processor_power_init_bm_check(struct
 						      acpi_processor_flags
 						      *flags, unsigned int cpu)
 {
 	flags->bm_check = 1;
+	return;
+}
+static inline int acpi_processor_ffh_cstate_probe(unsigned int cpu,
+		struct acpi_processor_cx *cx, struct acpi_power_register *reg)
+{
+	return -1;
+}
+static inline void acpi_processor_ffh_cstate_enter(
+		struct acpi_processor_cx *cstate)
+{
 	return;
 }
 #endif

include/asm-i386/processor.h

···
 		: :"a" (eax), "c" (ecx));
 }
 
+extern void mwait_idle_with_hints(unsigned long eax, unsigned long ecx);
+
 /* from system description table in BIOS.  Mostly for MCA use, but
 others may find it useful. */
 extern unsigned int machine_id;

include/asm-x86_64/processor.h

···
 		: :"a" (eax), "c" (ecx));
 }
 
+extern void mwait_idle_with_hints(unsigned long eax, unsigned long ecx);
+
 #define stack_current() \
 ({								\
 	struct thread_info *ti;					\