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author | Alok Kataria <akataria@vmware.com> | 2010-03-11 22:00:16 (GMT) |
---|---|---|
committer | H. Peter Anvin <hpa@zytor.com> | 2010-04-01 22:21:48 (GMT) |
commit | b4a5e8a1deca7e61ebaffb37344766b0f0e9f327 (patch) | |
tree | 9b396c3ddca5278d553448043c276fad528fcd93 /arch/x86/kernel/hpet.c | |
parent | 8da854cb02156c90028233ae1e85ce46a1d3f82c (diff) | |
download | linux-fsl-qoriq-b4a5e8a1deca7e61ebaffb37344766b0f0e9f327.tar.xz |
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 <akataria@vmware.com>
LKML-Reference: <201003112200.o2BM0Hre012875@imap1.linux-foundation.org>
Signed-off-by: Daniel Hecht <dhecht@vmware.com>
Cc: Venkatesh Pallipadi <venkatesh.pallipadi@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Diffstat (limited to 'arch/x86/kernel/hpet.c')
-rw-r--r-- | arch/x86/kernel/hpet.c | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c index 3d422da..2bda5f00 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; } |