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authorLen Brown <len.brown@intel.com>2010-07-22 17:23:10 -0400
committerLen Brown <len.brown@intel.com>2010-07-22 17:23:10 -0400
commitd3e7e99f2faf9f44ec0a3379f735b41c9173dfa1 (patch)
tree51b538d1463c37a596a8b34dd81845861d2b8ee8 /drivers
parent718be4aaf3613cf7c2d097f925abc3d3553c0605 (diff)
ACPI: create "processor.bm_check_disable" boot param
processor.bm_check_disable=1" prevents Linux from checking BM_STS before entering C3-type cpu power states. This may be useful for a system running acpi_idle where the BIOS exports FADT C-states, _CST IO C-states, or _CST FFH C-states with the BM_STS bit set; while configuring the chipset to set BM_STS more frequently than perhaps is optimal. Note that such systems may have been developed using a tickful OS that would quickly clear BM_STS, rather than a tickless OS that may go for some time between checking and clearing BM_STS. Note also that an alternative for newer systems is to use the intel_idle driver, which always ignores BM_STS, relying Linux device drivers to register constraints explicitly via PM_QOS. https://bugzilla.kernel.org/show_bug.cgi?id=15886 Signed-off-by: Len Brown <len.brown@intel.com>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/acpi/processor_idle.c5
1 files changed, 5 insertions, 0 deletions
diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index b351342f1faf..1d4104855296 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -76,6 +76,8 @@ static unsigned int max_cstate __read_mostly = ACPI_PROCESSOR_MAX_POWER;
module_param(max_cstate, uint, 0000);
static unsigned int nocst __read_mostly;
module_param(nocst, uint, 0000);
+static int bm_check_disable __read_mostly;
+module_param(bm_check_disable, uint, 0000);
static unsigned int latency_factor __read_mostly = 2;
module_param(latency_factor, uint, 0644);
@@ -763,6 +765,9 @@ static int acpi_idle_bm_check(void)
{
u32 bm_status = 0;
+ if (bm_check_disable)
+ return 0;
+
acpi_read_bit_register(ACPI_BITREG_BUS_MASTER_STATUS, &bm_status);
if (bm_status)
acpi_write_bit_register(ACPI_BITREG_BUS_MASTER_STATUS, 1);