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Linus Torvalds1da177e2005-04-16 15:20:36 -07001
2PowerNow! and Cool'n'Quiet are AMD names for frequency
3management capabilities in AMD processors. As the hardware
4implementation changes in new generations of the processors,
5there is a different cpu-freq driver for each generation.
6
7Note that the driver's will not load on the "wrong" hardware,
8so it is safe to try each driver in turn when in doubt as to
9which is the correct driver.
10
11Note that the functionality to change frequency (and voltage)
12is not available in all processors. The drivers will refuse
13to load on processors without this capability. The capability
14is detected with the cpuid instruction.
15
16The drivers use BIOS supplied tables to obtain frequency and
17voltage information appropriate for a particular platform.
18Frequency transitions will be unavailable if the BIOS does
19not supply these tables.
20
216th Generation: powernow-k6
22
237th Generation: powernow-k7: Athlon, Duron, Geode.
24
258th Generation: powernow-k8: Athlon, Athlon 64, Opteron, Sempron.
26Documentation on this functionality in 8th generation processors
27is available in the "BIOS and Kernel Developer's Guide", publication
2826094, in chapter 9, available for download from www.amd.com.
29
30BIOS supplied data, for powernow-k7 and for powernow-k8, may be
31from either the PSB table or from ACPI objects. The ACPI support
32is only available if the kernel config sets CONFIG_ACPI_PROCESSOR.
33The powernow-k8 driver will attempt to use ACPI if so configured,
34and fall back to PST if that fails.
35The powernow-k7 driver will try to use the PSB support first, and
36fall back to ACPI if the PSB support fails. A module parameter,
37acpi_force, is provided to force ACPI support to be used instead
38of PSB support.