Documentation/frv/clock.txt

   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.