mirror of
https://github.com/torvalds/linux.git
synced 2024-11-16 00:52:01 +00:00
66 lines
2.4 KiB
Plaintext
66 lines
2.4 KiB
Plaintext
|
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.
|