From: john stultz Currently the x86-64 HPET code assumes the entire HPET implementation from the spec is present. This breaks on boxes that do not implement the optional legacy timer replacement functionality portion of the spec. This patch fixes this issue, allowing x86-64 systems that cannot use the HPET for the timer interrupt and RTC to still use the HPET as a time source. I've tested this patch on a system systems without HPET, with HPET but without legacy timer replacement, as well as HPET with legacy timer replacement. This version adds a minor check to cap the HPET counter value in gettimeoffset_hpet to avoid possible time inconsistencies. Please ignore the A2 version I sent to you earlier. Cc: Andi Kleen Signed-off-by: Andrew Morton --- arch/x86_64/kernel/time.c | 42 ++++++++++++++++++++++++++++-------------- 1 files changed, 28 insertions(+), 14 deletions(-) diff -puN arch/x86_64/kernel/time.c~x86_64-fix-hpet-for-systems-that-dont-support-legacy arch/x86_64/kernel/time.c --- 25/arch/x86_64/kernel/time.c~x86_64-fix-hpet-for-systems-that-dont-support-legacy 2005-04-26 03:46:23.670352952 -0700 +++ 25-akpm/arch/x86_64/kernel/time.c 2005-04-26 03:46:23.675352192 -0700 @@ -60,6 +60,7 @@ static int notsc __initdata = 0; unsigned int cpu_khz; /* TSC clocks / usec, not used here */ static unsigned long hpet_period; /* fsecs / HPET clock */ unsigned long hpet_tick; /* HPET clocks / interrupt */ +static int hpet_use_timer; unsigned long vxtime_hz = PIT_TICK_RATE; int report_lost_ticks; /* command line option */ unsigned long long monotonic_base; @@ -101,7 +102,9 @@ static inline unsigned int do_gettimeoff static inline unsigned int do_gettimeoffset_hpet(void) { - return ((hpet_readl(HPET_COUNTER) - vxtime.last) * vxtime.quot) >> 32; + /* cap counter read to one tick to avoid inconsistencies */ + unsigned long counter = hpet_readl(HPET_COUNTER) - vxtime.last; + return (min(counter,hpet_tick) * vxtime.quot) >> 32; } unsigned int (*do_gettimeoffset)(void) = do_gettimeoffset_tsc; @@ -297,7 +300,7 @@ unsigned long long monotonic_clock(void) last_offset = vxtime.last; base = monotonic_base; - this_offset = hpet_readl(HPET_T0_CMP) - hpet_tick; + this_offset = hpet_readl(HPET_COUNTER); } while (read_seqretry(&xtime_lock, seq)); offset = (this_offset - last_offset); @@ -373,7 +376,14 @@ static irqreturn_t timer_interrupt(int i write_seqlock(&xtime_lock); - if (vxtime.hpet_address) { + if (vxtime.hpet_address) + offset = hpet_readl(HPET_COUNTER); + + if (hpet_use_timer) { + /* if we're using the hpet timer functionality, + * we can more accurately know the counter value + * when the timer interrupt occured. + */ offset = hpet_readl(HPET_T0_CMP) - hpet_tick; delay = hpet_readl(HPET_COUNTER) - offset; } else { @@ -795,17 +805,18 @@ static int hpet_timer_stop_set_go(unsign * Set up timer 0, as periodic with first interrupt to happen at hpet_tick, * and period also hpet_tick. */ - - hpet_writel(HPET_TN_ENABLE | HPET_TN_PERIODIC | HPET_TN_SETVAL | + if (hpet_use_timer) { + hpet_writel(HPET_TN_ENABLE | HPET_TN_PERIODIC | HPET_TN_SETVAL | HPET_TN_32BIT, HPET_T0_CFG); - hpet_writel(hpet_tick, HPET_T0_CMP); - hpet_writel(hpet_tick, HPET_T0_CMP); /* AK: why twice? */ - + hpet_writel(hpet_tick, HPET_T0_CMP); + hpet_writel(hpet_tick, HPET_T0_CMP); /* AK: why twice? */ + cfg |= HPET_CFG_LEGACY; + } /* * Go! */ - cfg |= HPET_CFG_ENABLE | HPET_CFG_LEGACY; + cfg |= HPET_CFG_ENABLE; hpet_writel(cfg, HPET_CFG); return 0; @@ -826,8 +837,7 @@ static int hpet_init(void) id = hpet_readl(HPET_ID); - if (!(id & HPET_ID_VENDOR) || !(id & HPET_ID_NUMBER) || - !(id & HPET_ID_LEGSUP)) + if (!(id & HPET_ID_VENDOR) || !(id & HPET_ID_NUMBER)) return -1; hpet_period = hpet_readl(HPET_PERIOD); @@ -837,6 +847,8 @@ static int hpet_init(void) hpet_tick = (1000000000L * (USEC_PER_SEC / HZ) + hpet_period / 2) / hpet_period; + hpet_use_timer = (id & HPET_ID_LEGSUP); + return hpet_timer_stop_set_go(hpet_tick); } @@ -893,9 +905,11 @@ void __init time_init(void) set_normalized_timespec(&wall_to_monotonic, -xtime.tv_sec, -xtime.tv_nsec); - if (!hpet_init()) { + if (!hpet_init()) vxtime_hz = (1000000000000000L + hpet_period / 2) / hpet_period; + + if (hpet_use_timer) { cpu_khz = hpet_calibrate_tsc(); timename = "HPET"; } else { @@ -948,12 +962,12 @@ void __init time_init_gtod(void) if (oem_force_hpet_timer()) notsc = 1; if (vxtime.hpet_address && notsc) { - timetype = "HPET"; + timetype = hpet_use_timer ? "HPET" : "PIT/HPET"; vxtime.last = hpet_readl(HPET_T0_CMP) - hpet_tick; vxtime.mode = VXTIME_HPET; do_gettimeoffset = do_gettimeoffset_hpet; } else { - timetype = vxtime.hpet_address ? "HPET/TSC" : "PIT/TSC"; + timetype = hpet_use_timer ? "HPET/TSC" : "PIT/TSC"; vxtime.mode = VXTIME_TSC; } _