Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1 | Clock scaling |
| 2 | ------------- |
| 3 | |
| 4 | The kernel supports scaling of CLCK.CMODE, CLCK.CM and CLKC.P0 clock |
| 5 | registers. If built with CONFIG_PM and CONFIG_SYSCTL options enabled, four |
| 6 | extra files will appear in the directory /proc/sys/pm/. Reading these files |
| 7 | will show: |
| 8 | |
| 9 | p0 -- current value of the P0 bit in CLKC register. |
| 10 | cm -- current value of the CM bits in CLKC register. |
| 11 | cmode -- current value of the CMODE bits in CLKC register. |
| 12 | |
| 13 | On all boards, the 'p0' file should also be writable, and either '1' or '0' |
| 14 | can be rewritten, to set or clear the CLKC_P0 bit respectively, hence |
| 15 | controlling whether the resource bus rate clock is halved. |
| 16 | |
| 17 | The 'cm' file should also be available on all boards. '0' can be written to it |
| 18 | to shift the board into High-Speed mode (normal), and '1' can be written to |
| 19 | shift the board into Medium-Speed mode. Selecting Low-Speed mode is not |
| 20 | supported by this interface, even though some CPUs do support it. |
| 21 | |
| 22 | On the boards with FR405 CPU (i.e. CB60 and CB70), the 'cmode' file is also |
| 23 | writable, allowing the CPU core speed (and other clock speeds) to be |
| 24 | controlled from userspace. |
| 25 | |
| 26 | |
| 27 | Determining current and possible settings |
| 28 | ----------------------------------------- |
| 29 | |
| 30 | The current state and the available masks can be found in /proc/cpuinfo. For |
| 31 | example, on the CB70: |
| 32 | |
| 33 | # cat /proc/cpuinfo |
| 34 | CPU-Series: fr400 |
| 35 | CPU-Core: fr405, gr0-31, BE, CCCR |
| 36 | CPU: mb93405 |
| 37 | MMU: Prot |
| 38 | FP-Media: fr0-31, Media |
| 39 | System: mb93091-cb70, mb93090-mb00 |
| 40 | PM-Controls: cmode=0xd31f, cm=0x3, p0=0x3, suspend=0x9 |
| 41 | PM-Status: cmode=3, cm=0, p0=0 |
| 42 | Clock-In: 50.00 MHz |
| 43 | Clock-Core: 300.00 MHz |
| 44 | Clock-SDRAM: 100.00 MHz |
| 45 | Clock-CBus: 100.00 MHz |
| 46 | Clock-Res: 50.00 MHz |
| 47 | Clock-Ext: 50.00 MHz |
| 48 | Clock-DSU: 25.00 MHz |
| 49 | BogoMips: 300.00 |
| 50 | |
| 51 | And on the PDK, the PM lines look like the following: |
| 52 | |
| 53 | PM-Controls: cm=0x3, p0=0x3, suspend=0x9 |
| 54 | PM-Status: cmode=9, cm=0, p0=0 |
| 55 | |
| 56 | The PM-Controls line, if present, will indicate which /proc/sys/pm files can |
| 57 | be set to what values. The specification values are bitmasks; so, for example, |
| 58 | "suspend=0x9" indicates that 0 and 3 can be written validly to |
| 59 | /proc/sys/pm/suspend. |
| 60 | |
| 61 | The PM-Controls line will only be present if CONFIG_PM is configured to Y. |
| 62 | |
| 63 | The PM-Status line indicates which clock controls are set to which value. If |
| 64 | the file can be read, then the suspend value must be 0, and so that's not |
| 65 | included. |