[PATCH][VIVID] x86/platform, acpi: Bypass legacy PIC and PIT in ACPI hardware reduced mode

[Colin King]

From: "Li, Aubrey" <aubrey.li at linux.intel.com>

On a platform in ACPI Hardware-reduced mode, the legacy PIC and
PIT may not be initialized even though they may be present in
silicon. Touching these legacy components causes unexpected
results on the system.

On the Bay Trail-T(ASUS-T100) platform, touching these legacy
components blocks platform hardware low idle power state(S0ix)
during system suspend. So we should bypass them in ACPI hardware
reduced mode.

Suggested-by: Arjan van de Ven <arjan at linux.intel.com>
Signed-off-by: Li Aubrey <aubrey.li at linux.intel.com>
Cc: <alan at linux.intel.com>
Cc: Alan Cox <alan at linux.intel.com>
Cc: H. Peter Anvin <hpa at linux.intel.com>
Cc: Len Brown <len.brown at intel.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Cc: Rafael J. Wysocki <rjw at rjwysocki.net>
Link: http://lkml.kernel.org/r/54FFF81C.20703@linux.intel.com
Signed-off-by: Ingo Molnar <mingo at kernel.org>
(cherry picked from upstream commit 7486341a98f26857f383aec88ffa10950087c3a1)
Signed-off-by: Colin Ian King <colin.king at canonical.com>
---
 arch/x86/kernel/acpi/boot.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index 3d525c6..803b684 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -1338,6 +1338,26 @@ static int __init dmi_ignore_irq0_timer_override(const struct dmi_system_id *d)
 }
 
 /*
+ * ACPI offers an alternative platform interface model that removes
+ * ACPI hardware requirements for platforms that do not implement
+ * the PC Architecture.
+ *
+ * We initialize the Hardware-reduced ACPI model here:
+ */
+static void __init acpi_reduced_hw_init(void)
+{
+	if (acpi_gbl_reduced_hardware) {
+		/*
+		 * Override x86_init functions and bypass legacy pic
+		 * in Hardware-reduced ACPI mode
+		 */
+		x86_init.timers.timer_init	= x86_init_noop;
+		x86_init.irqs.pre_vector_init	= x86_init_noop;
+		legacy_pic			= &null_legacy_pic;
+	}
+}
+
+/*
  * If your system is blacklisted here, but you find that acpi=force
  * works for you, please contact linux-acpi at vger.kernel.org
  */
@@ -1536,6 +1556,11 @@ int __init early_acpi_boot_init(void)
 	 */
 	early_acpi_process_madt();
 
+	/*
+	 * Hardware-reduced ACPI mode initialization:
+	 */
+	acpi_reduced_hw_init();
+
 	return 0;
 }
 
-- 
2.1.4