Messages in this thread Patch in this message | | | Date | Mon, 6 Oct 2008 16:17:41 -0700 | From | Greg KH <> | Subject | [patch 19/28] x86: HPET: read back compare register before reading counter |
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2.6.25-stable review patch. If anyone has any objections, please let us know.
------------------ From: Thomas Gleixner <tglx@linutronix.de>
commit 72d43d9bc9210d24d09202eaf219eac09e17b339 upstream
After fixing the u32 thinko I sill had occasional hickups on ATI chipsets with small deltas. There seems to be a delay between writing the compare register and the transffer to the internal register which triggers the interrupt. Reading back the value makes sure, that it hit the internal match register befor we compare against the counter value.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- arch/x86/kernel/hpet.c | 7 +++++++ 1 file changed, 7 insertions(+)
--- a/arch/x86/kernel/hpet.c +++ b/arch/x86/kernel/hpet.c @@ -290,6 +290,13 @@ static int hpet_legacy_next_event(unsign cnt += (u32) delta; hpet_writel(cnt, HPET_T0_CMP); + /* + * We need to read back the CMP register to make sure that + * what we wrote hit the chip before we compare it to the + * counter. + */ + WARN_ON((u32)hpet_readl(HPET_T0_CMP) != cnt); + return (s32)((u32)hpet_readl(HPET_COUNTER) - cnt) >= 0 ? -ETIME : 0; } --
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