Re: [PATCH] X86_64: fix hpet for systems that don't support legacy replacement (v. A3)

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Re: [PATCH] X86_64: fix hpet for systems that don't support legacy replacement (v. A3)

Vojtech Pavlik
On Fri, Apr 22, 2005 at 07:48:47PM -0700, john stultz wrote:

> Andrew, All,
> 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.
>
> Please consider for your tree.

I'd very much prefer if we could simply use the regular non-legacy HPET
interrupts for timer interrupt generation on both systems without HPET
legacy IRQ routing support than using this workaround.

It'd fix RTC interrupt issues on machines that do have HPET IRQ legacy
routing as well.

Did you give this option a consideration?

Other than that, the patch looks sane.

> thanks
> -john
>
> Changelog:
> A0: First sent to lkml
> A1: Implemented suggestions from Venkatesh
> A2: Whitespace cleanup.
> A3: Cap gettimeoffset_hpet to avoid time inconsistencies
>
> linux-2.6.12-rc2_x86-64_hpet_nolegacy-fix_A3.patch
> ==================================================
> diff -Nru a/arch/x86_64/kernel/time.c b/arch/x86_64/kernel/time.c
> --- a/arch/x86_64/kernel/time.c 2005-04-22 19:41:09 -07:00
> +++ b/arch/x86_64/kernel/time.c 2005-04-22 19:41:09 -07:00
> @@ -60,6 +60,7 @@
>  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_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 @@
>  
>   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 @@
>  
>   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 {
> @@ -794,17 +804,18 @@
>   * 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;
> @@ -825,8 +836,7 @@
>  
>   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);
> @@ -836,6 +846,8 @@
>   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);
>  }
>  
> @@ -892,9 +904,11 @@
>   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 {
> @@ -940,12 +954,12 @@
>   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;
>   }
>  
>
>
>

--
Vojtech Pavlik
SuSE Labs, SuSE CR
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