| 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. |