diff options
| -rw-r--r-- | drivers/Kconfig | 3 | ||||
| -rw-r--r-- | drivers/clocksource/Kconfig | 2 | ||||
| -rw-r--r-- | drivers/clocksource/Makefile | 1 | ||||
| -rw-r--r-- | drivers/clocksource/i8253.c | 88 |
4 files changed, 94 insertions, 0 deletions
diff --git a/drivers/Kconfig b/drivers/Kconfig index 177c7d15693..557a469c7aa 100644 --- a/drivers/Kconfig +++ b/drivers/Kconfig @@ -119,4 +119,7 @@ source "drivers/platform/Kconfig" source "drivers/clk/Kconfig" source "drivers/hwspinlock/Kconfig" + +source "drivers/clocksource/Kconfig" + endmenu diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig new file mode 100644 index 00000000000..110aeeb52f9 --- /dev/null +++ b/drivers/clocksource/Kconfig @@ -0,0 +1,2 @@ +config CLKSRC_I8253 + bool diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile index be61ece6330..cfb6383b543 100644 --- a/drivers/clocksource/Makefile +++ b/drivers/clocksource/Makefile @@ -6,3 +6,4 @@ obj-$(CONFIG_CS5535_CLOCK_EVENT_SRC) += cs5535-clockevt.o obj-$(CONFIG_SH_TIMER_CMT) += sh_cmt.o obj-$(CONFIG_SH_TIMER_MTU2) += sh_mtu2.o obj-$(CONFIG_SH_TIMER_TMU) += sh_tmu.o +obj-$(CONFIG_CLKSRC_I8253) += i8253.o diff --git a/drivers/clocksource/i8253.c b/drivers/clocksource/i8253.c new file mode 100644 index 00000000000..225c1761b37 --- /dev/null +++ b/drivers/clocksource/i8253.c @@ -0,0 +1,88 @@ +/* + * i8253 PIT clocksource + */ +#include <linux/clocksource.h> +#include <linux/init.h> +#include <linux/io.h> +#include <linux/spinlock.h> +#include <linux/timex.h> + +#include <asm/i8253.h> + +/* + * Since the PIT overflows every tick, its not very useful + * to just read by itself. So use jiffies to emulate a free + * running counter: + */ +static cycle_t i8253_read(struct clocksource *cs) +{ + static int old_count; + static u32 old_jifs; + unsigned long flags; + int count; + u32 jifs; + + raw_spin_lock_irqsave(&i8253_lock, flags); + /* + * Although our caller may have the read side of xtime_lock, + * this is now a seqlock, and we are cheating in this routine + * by having side effects on state that we cannot undo if + * there is a collision on the seqlock and our caller has to + * retry. (Namely, old_jifs and old_count.) So we must treat + * jiffies as volatile despite the lock. We read jiffies + * before latching the timer count to guarantee that although + * the jiffies value might be older than the count (that is, + * the counter may underflow between the last point where + * jiffies was incremented and the point where we latch the + * count), it cannot be newer. + */ + jifs = jiffies; + outb_pit(0x00, PIT_MODE); /* latch the count ASAP */ + count = inb_pit(PIT_CH0); /* read the latched count */ + count |= inb_pit(PIT_CH0) << 8; + + /* VIA686a test code... reset the latch if count > max + 1 */ + if (count > LATCH) { + outb_pit(0x34, PIT_MODE); + outb_pit(PIT_LATCH & 0xff, PIT_CH0); + outb_pit(PIT_LATCH >> 8, PIT_CH0); + count = PIT_LATCH - 1; + } + + /* + * It's possible for count to appear to go the wrong way for a + * couple of reasons: + * + * 1. The timer counter underflows, but we haven't handled the + * resulting interrupt and incremented jiffies yet. + * 2. Hardware problem with the timer, not giving us continuous time, + * the counter does small "jumps" upwards on some Pentium systems, + * (see c't 95/10 page 335 for Neptun bug.) + * + * Previous attempts to handle these cases intelligently were + * buggy, so we just do the simple thing now. + */ + if (count > old_count && jifs == old_jifs) + count = old_count; + + old_count = count; + old_jifs = jifs; + + raw_spin_unlock_irqrestore(&i8253_lock, flags); + + count = (PIT_LATCH - 1) - count; + + return (cycle_t)(jifs * PIT_LATCH) + count; +} + +static struct clocksource i8253_cs = { + .name = "pit", + .rating = 110, + .read = i8253_read, + .mask = CLOCKSOURCE_MASK(32), +}; + +int __init clocksource_i8253_init(void) +{ + return clocksource_register_hz(&i8253_cs, PIT_TICK_RATE); +} |