[PATCH] ACPI: create "processor.bm_check_disable" boot param
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From: Len Brown on 22 Jul 2010 17:50 From: Len Brown <len.brown(a)intel.com> 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(a)intel.com> --- 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 b351342..1d41048 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); -- 1.7.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |