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Commit | Line | Data |
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1da177e4 LT |
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. |