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>
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@ -76,6 +76,8 @@ static unsigned int max_cstate __read_mostly = ACPI_PROCESSOR_MAX_POWER;
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module_param(max_cstate, uint, 0000);
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static unsigned int nocst __read_mostly;
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module_param(nocst, uint, 0000);
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static int bm_check_disable __read_mostly;
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module_param(bm_check_disable, uint, 0000);
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static unsigned int latency_factor __read_mostly = 2;
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module_param(latency_factor, uint, 0644);
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@ -763,6 +765,9 @@ static int acpi_idle_bm_check(void)
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{
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u32 bm_status = 0;
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if (bm_check_disable)
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return 0;
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acpi_read_bit_register(ACPI_BITREG_BUS_MASTER_STATUS, &bm_status);
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if (bm_status)
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acpi_write_bit_register(ACPI_BITREG_BUS_MASTER_STATUS, 1);
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