From b4a5e8a1deca7e61ebaffb37344766b0f0e9f327 Mon Sep 17 00:00:00 2001 From: Alok Kataria Date: Thu, 11 Mar 2010 14:00:16 -0800 Subject: [PATCH] x86, hpet: Fix bug in RTC emulation We think there exists a bug in the HPET code that emulates the RTC. In the normal case, when the RTC frequency is set, the rtc driver tells the hpet code about it here: int hpet_set_periodic_freq(unsigned long freq) { uint64_t clc; if (!is_hpet_enabled()) return 0; if (freq <= DEFAULT_RTC_INT_FREQ) hpet_pie_limit = DEFAULT_RTC_INT_FREQ / freq; else { clc = (uint64_t) hpet_clockevent.mult * NSEC_PER_SEC; do_div(clc, freq); clc >>= hpet_clockevent.shift; hpet_pie_delta = (unsigned long) clc; } return 1; } If freq is set to 64Hz (DEFAULT_RTC_INT_FREQ) or lower, then hpet_pie_limit (a static) is set to non-zero. Then, on every one-shot HPET interrupt, hpet_rtc_timer_reinit is called to compute the next timeout. Well, that function has this logic: if (!(hpet_rtc_flags & RTC_PIE) || hpet_pie_limit) delta = hpet_default_delta; else delta = hpet_pie_delta; Since hpet_pie_limit is not 0, hpet_default_delta is used. That corresponds to 64Hz. Now, if you set a different rtc frequency, you'll take the else path through hpet_set_periodic_freq, but unfortunately no one resets hpet_pie_limit back to 0. Boom....now you are stuck with 64Hz RTC interrupts forever. The patch below just resets the hpet_pie_limit value when requested freq is greater than DEFAULT_RTC_INT_FREQ, which we think fixes this problem. Signed-off-by: Alok N Kataria LKML-Reference: <201003112200.o2BM0Hre012875@imap1.linux-foundation.org> Signed-off-by: Daniel Hecht Cc: Venkatesh Pallipadi Cc: Thomas Gleixner Cc: "H. Peter Anvin" Cc: Ingo Molnar Signed-off-by: Andrew Morton Signed-off-by: H. Peter Anvin --- arch/x86/kernel/hpet.c | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c index 3d422da92100..2bda5f0052f7 100644 --- a/arch/x86/kernel/hpet.c +++ b/arch/x86/kernel/hpet.c @@ -1149,6 +1149,7 @@ int hpet_set_periodic_freq(unsigned long freq) do_div(clc, freq); clc >>= hpet_clockevent.shift; hpet_pie_delta = clc; + hpet_pie_limit = 0; } return 1; } -- 2.39.2