From 89c0b8e2520e12d69dafc663dfbd39f8180438ea Mon Sep 17 00:00:00 2001 From: Russell King Date: Sun, 8 May 2011 18:47:58 +0100 Subject: clocksource: add common i8253 PIT clocksource This is based upon both arch/arm/mach-footbridge/isa-timer.c and arch/x86/kernel/i8253.c. Acked-by: John Stultz Acked-by: Thomas Gleixner Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: Ralf Baechle Signed-off-by: Russell King --- drivers/clocksource/Kconfig | 2 + drivers/clocksource/Makefile | 1 + drivers/clocksource/i8253.c | 88 ++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 91 insertions(+) create mode 100644 drivers/clocksource/Kconfig create mode 100644 drivers/clocksource/i8253.c (limited to 'drivers/clocksource') diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig new file mode 100644 index 0000000..110aeeb --- /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 be61ece..cfb6383 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 0000000..225c176 --- /dev/null +++ b/drivers/clocksource/i8253.c @@ -0,0 +1,88 @@ +/* + * i8253 PIT clocksource + */ +#include +#include +#include +#include +#include + +#include + +/* + * 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); +} -- cgit v1.1