39 lines
1.6 KiB
Text
39 lines
1.6 KiB
Text
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PowerNow! and Cool'n'Quiet are AMD names for frequency
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management capabilities in AMD processors. As the hardware
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implementation changes in new generations of the processors,
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there is a different cpu-freq driver for each generation.
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Note that the driver's will not load on the "wrong" hardware,
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so it is safe to try each driver in turn when in doubt as to
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which is the correct driver.
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Note that the functionality to change frequency (and voltage)
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is not available in all processors. The drivers will refuse
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to load on processors without this capability. The capability
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is detected with the cpuid instruction.
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The drivers use BIOS supplied tables to obtain frequency and
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voltage information appropriate for a particular platform.
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Frequency transitions will be unavailable if the BIOS does
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not supply these tables.
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6th Generation: powernow-k6
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7th Generation: powernow-k7: Athlon, Duron, Geode.
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8th Generation: powernow-k8: Athlon, Athlon 64, Opteron, Sempron.
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Documentation on this functionality in 8th generation processors
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is available in the "BIOS and Kernel Developer's Guide", publication
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26094, in chapter 9, available for download from www.amd.com.
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BIOS supplied data, for powernow-k7 and for powernow-k8, may be
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from either the PSB table or from ACPI objects. The ACPI support
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is only available if the kernel config sets CONFIG_ACPI_PROCESSOR.
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The powernow-k8 driver will attempt to use ACPI if so configured,
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and fall back to PST if that fails.
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The powernow-k7 driver will try to use the PSB support first, and
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fall back to ACPI if the PSB support fails. A module parameter,
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acpi_force, is provided to force ACPI support to be used instead
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of PSB support.
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