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Diffstat (limited to 'kernel/Documentation/frv/clock.txt')
| -rw-r--r-- | kernel/Documentation/frv/clock.txt | 65 |
1 files changed, 65 insertions, 0 deletions
diff --git a/kernel/Documentation/frv/clock.txt b/kernel/Documentation/frv/clock.txt new file mode 100644 index 000000000..c72d350e1 --- /dev/null +++ b/kernel/Documentation/frv/clock.txt @@ -0,0 +1,65 @@ +Clock scaling +------------- + +The kernel supports scaling of CLCK.CMODE, CLCK.CM and CLKC.P0 clock +registers. If built with CONFIG_PM and CONFIG_SYSCTL options enabled, four +extra files will appear in the directory /proc/sys/pm/. Reading these files +will show: + + p0 -- current value of the P0 bit in CLKC register. + cm -- current value of the CM bits in CLKC register. + cmode -- current value of the CMODE bits in CLKC register. + +On all boards, the 'p0' file should also be writable, and either '1' or '0' +can be rewritten, to set or clear the CLKC_P0 bit respectively, hence +controlling whether the resource bus rate clock is halved. + +The 'cm' file should also be available on all boards. '0' can be written to it +to shift the board into High-Speed mode (normal), and '1' can be written to +shift the board into Medium-Speed mode. Selecting Low-Speed mode is not +supported by this interface, even though some CPUs do support it. + +On the boards with FR405 CPU (i.e. CB60 and CB70), the 'cmode' file is also +writable, allowing the CPU core speed (and other clock speeds) to be +controlled from userspace. + + +Determining current and possible settings +----------------------------------------- + +The current state and the available masks can be found in /proc/cpuinfo. For +example, on the CB70: + + # cat /proc/cpuinfo + CPU-Series: fr400 + CPU-Core: fr405, gr0-31, BE, CCCR + CPU: mb93405 + MMU: Prot + FP-Media: fr0-31, Media + System: mb93091-cb70, mb93090-mb00 + PM-Controls: cmode=0xd31f, cm=0x3, p0=0x3, suspend=0x9 + PM-Status: cmode=3, cm=0, p0=0 + Clock-In: 50.00 MHz + Clock-Core: 300.00 MHz + Clock-SDRAM: 100.00 MHz + Clock-CBus: 100.00 MHz + Clock-Res: 50.00 MHz + Clock-Ext: 50.00 MHz + Clock-DSU: 25.00 MHz + BogoMips: 300.00 + +And on the PDK, the PM lines look like the following: + + PM-Controls: cm=0x3, p0=0x3, suspend=0x9 + PM-Status: cmode=9, cm=0, p0=0 + +The PM-Controls line, if present, will indicate which /proc/sys/pm files can +be set to what values. The specification values are bitmasks; so, for example, +"suspend=0x9" indicates that 0 and 3 can be written validly to +/proc/sys/pm/suspend. + +The PM-Controls line will only be present if CONFIG_PM is configured to Y. + +The PM-Status line indicates which clock controls are set to which value. If +the file can be read, then the suspend value must be 0, and so that's not +included. |