[MIPS] lib_mips/time.c: Fix CP0 count register usage and timer routines

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>

1 files changed, 25 insertions, 6 deletions

diff --git a/lib_mips/time.c b/lib_mips/time.c
index fe36530..1e92789 100644
--- a/lib_mips/time.c
+++ b/lib_mips/time.c
@@ -24,31 +24,50 @@
 #include <common.h>
 #include <asm/mipsregs.h>
 
+static unsigned long timestamp;
+
+/* how many counter cycles in a jiffy */
+#define CYCLES_PER_JIFFY	(CFG_MIPS_TIMER_FREQ + CFG_HZ / 2) / CFG_HZ
+
 /*
  * timer without interrupts
  */
 
 int timer_init(void)
 {
-	write_c0_compare(0);
-	write_c0_count(0);
+	/* Set up the timer for the first expiration. */
+	timestamp = 0;
+	write_c0_compare(read_c0_count() + CYCLES_PER_JIFFY);
 
 	return 0;
 }
 
 void reset_timer(void)
 {
-	write_c0_count(0);
+	timestamp = 0;
+	write_c0_compare(read_c0_count() + CYCLES_PER_JIFFY);
 }
 
 ulong get_timer(ulong base)
 {
-	return read_c0_count() - base;
+	unsigned int count;
+	unsigned int expirelo = read_c0_compare();
+
+	/* Check to see if we have missed any timestamps. */
+	count = read_c0_count();
+	while ((count - expirelo) < 0x7fffffff) {
+		expirelo += CYCLES_PER_JIFFY;
+		timestamp++;
+	}
+	write_c0_compare(expirelo);
+
+	return (timestamp - base);
 }
 
 void set_timer(ulong t)
 {
-	write_c0_count(t);
+	timestamp = t;
+	write_c0_compare(read_c0_count() + CYCLES_PER_JIFFY);
 }
 
 void udelay(unsigned long usec)
@@ -66,7 +85,7 @@ void udelay(unsigned long usec)
  */
 unsigned long long get_ticks(void)
 {
-	return read_c0_count();
+	return get_timer(0);
 }
 
 /*