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| author | Len Brown <len.brown@intel.com> | 2010-07-22 17:23:10 -0400 |
|---|---|---|
| committer | Len Brown <len.brown@intel.com> | 2010-07-22 17:23:10 -0400 |
| commit | d3e7e99f2faf9f44ec0a3379f735b41c9173dfa1 (patch) | |
| tree | 51b538d1463c37a596a8b34dd81845861d2b8ee8 /drivers | |
| parent | 718be4aaf3613cf7c2d097f925abc3d3553c0605 (diff) | |
| download | linux-d3e7e99f2faf9f44ec0a3379f735b41c9173dfa1.tar.gz linux-d3e7e99f2faf9f44ec0a3379f735b41c9173dfa1.tar.bz2 linux-d3e7e99f2faf9f44ec0a3379f735b41c9173dfa1.zip | |
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.c | 5 |
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); |