linux-kernel - Re: [PATCH] x86, HPET: ignore any PCI BARs that match an HPET we already know about

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Message-ID: <4C9A6D83.6090301@zytor.com>
Date:	Wed, 22 Sep 2010 13:56:35 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Bjorn Helgaas <bjorn.helgaas@...com>
CC:	Venkatesh Pallipadi <venki@...gle.com>,
	Prarit Bhargava <prarit@...hat.com>,
	Simon Arlott <simon@...e.lp0.eu>, x86@...nel.org,
	Clemens Ladisch <clemens@...isch.de>,
	linux-kernel@...r.kernel.org, Marc Jones <marcj303@...il.com>,
	Jordan Crouse <jcrouse@...eaurora.org>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86, HPET: ignore any PCI BARs that match an HPET we
 already know about

On 09/22/2010 01:21 PM, H. Peter Anvin wrote:
> On 09/22/2010 01:19 PM, Bjorn Helgaas wrote:
>> On Wednesday, September 22, 2010 02:15:47 pm Bjorn Helgaas wrote:
>>>
>>> We often discover the HPET early, via the static ACPI HPET table, before
>>> enumerating PCI devices.  If the HPET is implemented as a PCI function,
>>> we will discover it again during PCI device enumeration.  We must ignore
>>> the PCI function so we don't inadvertently move it out from under the
>>> driver.
>>>
>>> I think it's better to ignore *any* PCI BAR that matches a previously
>>> discovered HPET; that way we don't need platform-specific knowledge,
>>> and we won't have to add more quirks for future machines.
>>>
>>> This is for a regression from 2.6.34, but the reporter has been
>>> unable to test it yet.
>>>
>>> Reference: https://bugzilla.kernel.org/show_bug.cgi?id=18482
>>
>> I've tried hard to find somebody who can test this, but nobody who
>> can reproduce the original failure has been able to test it.  I
>> propose that we put it in linux-next and see what happens there.
>>
> 
> Makes sense to me.
> 

Actually, this ties into something that I have pointed out in the past:
there will be devices used by the firmware or the platform that has
corresponding PCI BARs. Most of them can be spotted by being a PCI BAR
pointing into reserved memory.

When we find a PCI BAR pointing into reserved memory it really should be
considered a fixed resource, period, full stop.  This is critical for
the proper operation of the platform.

	-hpa

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