MIPS port has two problems in timer routines. One is now we assume CFG_HZ
equals to CP0 counter frequency, but this is wrong. CFG_HZ has to be 1000
in the U-Boot system.
The other is we don't have a proper time management counter like timestamp
other ARCHs have. We need the 32-bit millisecond clock counter.
This patch introduces timestamp and CYCLES_PER_JIFFY. timestamp is a
32-bit non-overflowing CFG_HZ counter, and CYCLES_PER_JIFFY is the number
of calculated CP0 counter cycles in a CFG_HZ.
STRATEGY:
* Fix improper CFG_HZ value to have 1000
* Use CFG_MIPS_TIMER_FREQ for timer counter frequency, instead.
* timer_init: initialize timestamp and set up the first timer expiration.
Note that we don't need to initialize CP0 count/compare registers here
as they have been already zeroed out on the system reset. Leave them as
they are.
* get_timer: calculate how many timestamps have been passed, then return
base-relative timestamp. Make sure we can easily count missed timestamps
regardless of CP0 count/compare value.
* get_ticks: return the current timestamp, that is get_timer(0).
Most parts are from good old Linux v2.6.16 kernel.
v2:
- Remove FIXME comments as they turned out to be trivial.
- Use CP0 compare register as a global variable for expirelo.
- Kill a global variable 'cycles_per_jiffy'. Use #define CYCLES_PER_JIFFY
instead.
Signed-off-by: Shinya Kuribayashi <skuribay@ruby.dti.ne.jp>