[PATCH] ACPI: make acpi_idle Nehalem-aware

[Len Brown <lenb@kernel.org>]

From: Len Brown <len.brown@intel.com>

The BIOS exports deep C-states on modern Intel processors
as "C3-type" to satisfy various legacy Operating Systems.

However, the hardware actually supports C2-type, and does
not require the extra costs of C3-type.

One of the costs is to check the BM_STS (Bus Master Status)
bit before entering C3, and instead choose a shallower C-state
if there was "recent bus master activity".

We have found a number of systems in the field that erroneously
set BM_STS and prevent entry into deep C-states.
Re-define BIOS presented C3-type states as C2-type states
on modern processors to avoid this issue.

If a device in the system really does want to prevent use
of a deep C-state, its Linux driver should register its
constraints via pm_qos_add_request().

https://bugzilla.kernel.org/show_bug.cgi?id=15886

Signed-off-by: Len Brown <len.brown@intel.com>
---
 drivers/acpi/processor_idle.c |   38 ++++++++++++++++++++++++++++++++++++++
 1 files changed, 38 insertions(+), 0 deletions(-)

diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index b1b3856..14d1a0c 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -607,6 +607,38 @@ static void acpi_processor_power_verify_c3(struct acpi_processor *pr,
 	return;
 }
 
+/*
+ * Modern Intel processors support only ACPI C2-type C-states.
+ * But the BIOS tends to report its deepest C-state as C3-type
+ * to satisfy various old operating systems.  We can skip
+ * C3 OS overhead by treating the deep-states as C2-type.
+ * Also, we can avoid checking BM_STS, which on some systems
+ * erroneously prevents entry into C3-type states.
+ */
+static int acpi_c3type_is_really_c2type(void) {
+
+	if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
+		return 0;
+
+	if (boot_cpu_data.x86 != 6)
+		return 0;
+
+	switch(boot_cpu_data.x86_model) {
+	case 0x1A:	/* Core i7, Xeon 5500 series */
+	case 0x1E:	/* Core i7 and i5 Processor */
+	case 0x1F:	/* Core i7 and i5 Processor */
+	case 0x2E:	/* NHM-EX Xeon */
+	case 0x2F:	/* WSM-EX Xeon */
+	case 0x25:	/* WSM */
+	case 0x2C:	/* WSM */
+	case 0x2A:	/* SNB */
+	case 0x2D:	/* SNB Xeon */
+		return 1;
+	default:
+		return 0;
+	}
+}
+
 static int acpi_processor_power_verify(struct acpi_processor *pr)
 {
 	unsigned int i;
@@ -617,6 +649,12 @@ static int acpi_processor_power_verify(struct acpi_processor *pr)
 	for (i = 1; i < ACPI_PROCESSOR_MAX_POWER && i <= max_cstate; i++) {
 		struct acpi_processor_cx *cx = &pr->power.states[i];
 
+		if ((cx->type == ACPI_STATE_C3)
+			&& acpi_c3type_is_really_c2type()) {
+				ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Redefining C3-type to C2\n"));
+				cx->type = ACPI_STATE_C2;
+		}
+
 		switch (cx->type) {
 		case ACPI_STATE_C1:
 			cx->valid = 1;
-- 
1.7.2.rc3.43.g24e7a