linux-kernel - [PATCH] x86: fix hpet timer reinit for x86

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Date:	Wed, 04 Feb 2009 13:40:31 +0300
From:	Pavel Emelyanov <xemul@...nvz.org>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kirill Korotaev <dev@...nvz.org>
Subject: [PATCH] x86: fix hpet timer reinit for x86_64

There's a small problem with hpet_rtc_reinit function - it checks
for the
	hpet_readl(HPET_COUNTER) - hpet_t1_cmp > 0
to continue increasing both the HPET_T1_CMP (register) and the 
hpet_t1_cmp (variable).

But since the HPET_COUNTER is always 32-bit, if the hpet_t1_cmp
is 64-bit this condition will always be FALSE once the latter hits
the 32-bit boundary, and we can have a situation, when we don't
increase the HPET_T1_CMP register high enough.

The result - timer stops ticking, since HPET_T1_CMP becomes less, 
than the COUNTER and never increased again.

The solution is to cut the upper 32-bit from the hpet_t1_cmp
variable to make the comparison to HPET_COUNTER correct.

Reported-by: Kirill Korotaev <dev@...nvz.org>
Signed-off-by: Pavel Emelyanov <xemul@...nvz.org>

---

diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
index 64d5ad0..ec319d1 100644
--- a/arch/x86/kernel/hpet.c
+++ b/arch/x86/kernel/hpet.c
@@ -1075,7 +1075,7 @@ static void hpet_rtc_timer_reinit(void)
 		hpet_t1_cmp += delta;
 		hpet_writel(hpet_t1_cmp, HPET_T1_CMP);
 		lost_ints++;
-	} while ((long)(hpet_readl(HPET_COUNTER) - hpet_t1_cmp) > 0);
+	} while ((long)(hpet_readl(HPET_COUNTER) - (u32)hpet_t1_cmp) > 0);
 
 	if (lost_ints) {
 		if (hpet_rtc_flags & RTC_PIE)
--
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