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Based on kernel version 3.15.4. Page generated on 2014-07-07 09:03 EST.

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.
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