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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
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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+
+PowerNow! and Cool'n'Quiet are AMD names for frequency
+management capabilities in AMD processors. As the hardware
+implementation changes in new generations of the processors,
+there is a different cpu-freq driver for each generation.
+
+Note that the driver's will not load on the "wrong" hardware,
+so it is safe to try each driver in turn when in doubt as to
+which is the correct driver.
+
+Note that the functionality to change frequency (and voltage)
+is not available in all processors. The drivers will refuse
+to load on processors without this capability. The capability
+is detected with the cpuid instruction.
+
+The drivers use BIOS supplied tables to obtain frequency and
+voltage information appropriate for a particular platform.
+Frequency transitions will be unavailable if the BIOS does
+not supply these tables.
+
+6th Generation: powernow-k6
+
+7th Generation: powernow-k7: Athlon, Duron, Geode.
+
+8th Generation: powernow-k8: Athlon, Athlon 64, Opteron, Sempron.
+Documentation on this functionality in 8th generation processors
+is available in the "BIOS and Kernel Developer's Guide", publication
+26094, in chapter 9, available for download from www.amd.com.
+
+BIOS supplied data, for powernow-k7 and for powernow-k8, may be
+from either the PSB table or from ACPI objects. The ACPI support
+is only available if the kernel config sets CONFIG_ACPI_PROCESSOR.
+The powernow-k8 driver will attempt to use ACPI if so configured,
+and fall back to PST if that fails.
+The powernow-k7 driver will try to use the PSB support first, and
+fall back to ACPI if the PSB support fails. A module parameter,
+acpi_force, is provided to force ACPI support to be used instead
+of PSB support.