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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 18:20:36 -0400
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 18:20:36 -0400
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/cpu-freq/amd-powernow.txt
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
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1
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.