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

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Date:	Wed, 04 Feb 2009 14:51:43 +0300
From:	Pavel Emelyanov <xemul@...nvz.org>
To:	Vitaly Mayatskikh <v.mayatskih@...il.com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kirill Korotaev <dev@...nvz.org>
Subject: Re: [PATCH] x86: fix hpet timer reinit for x86_64

Vitaly Mayatskikh wrote:
> At Wed, 04 Feb 2009 13:40:31 +0300, Pavel Emelyanov wrote:
>> 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.
> 
> Why not to use u32 as a type for hpet_t1_cmp then?

That's the matter of taste from my POV, so I can re-send the patch
if x86 maintainers agree with your version.

> --
> wbr, Vitaly
> 

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