| |
| 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. |