linux-kernel - Re: [ PATCH] Add suspend/resume for HPET was: Re: [3/6] 2.6.21-rc4: known regressions

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Message-ID: <Pine.LNX.4.64.0703290930540.6730@woody.linux-foundation.org>
Date:	Thu, 29 Mar 2007 09:35:21 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Maxim <maximlevitsky@...il.com>
cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	Jeff Chua <jeff.chua.linux@...il.com>,
	Adrian Bunk <bunk@...sta.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, pavel@...e.cz,
	linux-pm@...ts.osdl.org, gregkh@...e.de,
	linux-pci@...ey.karlin.mff.cuni.cz,
	Jens Axboe <jens.axboe@...cle.com>,
	Len Brown <lenb@...nel.org>, linux-acpi@...r.kernel.org,
	jgarzik@...ox.com, linux-ide@...r.kernel.org,
	"Michael S. Tsirkin" <mst@...lanox.co.il>
Subject: Re: [ PATCH] Add suspend/resume for HPET was: Re: [3/6] 2.6.21-rc4:
 known regressions



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
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