From 718be4aaf3613cf7c2d097f925abc3d3553c0605 Mon Sep 17 00:00:00 2001 From: Len Brown Date: Thu, 22 Jul 2010 16:54:27 -0400 Subject: ACPI: skip checking BM_STS if the BIOS doesn't ask for it It turns out that there is a bit in the _CST for Intel FFH C3 that tells the OS if we should be checking BM_STS or not. Linux has been unconditionally checking BM_STS. If the chip-set is configured to enable BM_STS, it can retard or completely prevent entry into deep C-states -- as illustrated by turbostat: http://userweb.kernel.org/~lenb/acpi/utils/pmtools/turbostat/ ref: Intel Processor Vendor-Specific ACPI Interface Specification table 4 "_CST FFH GAS Field Encoding" Bit 1: Set to 1 if OSPM should use Bus Master avoidance for this C-state https://bugzilla.kernel.org/show_bug.cgi?id=15886 Signed-off-by: Len Brown --- drivers/acpi/processor_idle.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'drivers/acpi/processor_idle.c') diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c index b1b385692f4..b351342f1fa 100644 --- a/drivers/acpi/processor_idle.c +++ b/drivers/acpi/processor_idle.c @@ -947,7 +947,7 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev, if (acpi_idle_suspend) return(acpi_idle_enter_c1(dev, state)); - if (acpi_idle_bm_check()) { + if (!cx->bm_sts_skip && acpi_idle_bm_check()) { if (dev->safe_state) { dev->last_state = dev->safe_state; return dev->safe_state->enter(dev, dev->safe_state); -- cgit v1.2.3-18-g5258