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From: Maxim Levitsky <maximlevitsky@gmail.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [ PATCH] Add suspend/resume for HPET was: Re: [3/6] 2.6.21-rc4: known regressions
Date: Thu, 29 Mar 2007 18:51:18 +0200
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Cc: Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
       Jeff Chua <jeff.chua.linux@gmail.com>, Adrian Bunk <bunk@stusta.de>,
       Andrew Morton <akpm@linux-foundation.org>,
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       "Eric W. Biederman" <ebiederm@xmission.com>,
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       linux-pci@atrey.karlin.mff.cuni.cz, Jens Axboe <jens.axboe@oracle.com>,
       Len Brown <lenb@kernel.org>, linux-acpi@vger.kernel.org,
       jgarzik@pobox.com, linux-ide@vger.kernel.org,
       "Michael S. Tsirkin" <mst@mellanox.co.il>
References: <Pine.LNX.4.64.0703160925270.26106@woody.linux-foundation.org> <200703290747.28929.maximlevitsky@gmail.com> <Pine.LNX.4.64.0703290930540.6730@woody.linux-foundation.org>
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On Thursday 29 March 2007 18:35:21 Linus Torvalds wrote:
> 
> On Thu, 29 Mar 2007, Maxim wrote:
> 
> > On Thursday 29 March 2007 07:08:58 Linus Torvalds wrote:
> > > 
> > > (Or, better yet, shouldn't we set "boot_hpet_disable" when we decide not 
> > > to use the HPET, and set hpet_virt_address to NULL?)
> > 
> > This is done here
> > 
> > out_nohpet:
> > 	iounmap(hpet_virt_address);
> > 	hpet_virt_address = NULL;
> 
> No, that only clears hpet_virt_address, and thus makes all subsequent 
> "hpet_readl()" and "hpet_writel()" calls oops.
> 
> But it doesn't actually *tell* anybody that the HPET is disabled, so if 
> you later on do
> 
> 	if (is_hpet_capable()) {
> 		time = hpet_readl(..);
> 		..
> 
> you will just Oops!
> 
> So as far as I can see, even with your latest patch, if hpet_enable() 
> fails (and triggers the "goto out_nohpet" cases), you'll just oops 
> immediately when you try to suspend/resume the HPET.
> 
> THAT was what I meant - when we clear hpet_virt_address, we should also 
> tell all potential subsequent users that the HPET is not there!
> 
> 		Linus
> 

Hi,
	I agree, and as you said I did exactly that:

out_nohpet:
	iounmap(hpet_virt_address);
	hpet_virt_address = NULL;
	boot_hpet_disable = 1; <<<--- this ensures that is_hpet_capable() will never return positive value


	I also sent an updated version on my patch with subject line "[PATCH v2] Add suspend/resume for HPET"

	I forgot (a typo) to check error code in  hpet_register_sysfs
	Thanks to Sergei Shtylyov for pointing me on that.

	This patch should be ok.

	Best regards,
		Maxim Levitsky