linux-kernel - Re: [Patch 1/1] x86 pci: Add option to not assign BAR's if not already assigned

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Date:	Fri, 14 May 2010 16:32:07 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
CC:	Mike Travis <travis@....com>, Bjorn Helgaas <bjorn.helgaas@...com>,
	Mike Habeck <habeck@....com>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	Jacob Pan <jacob.jun.pan@...el.com>, Tejun Heo <tj@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Yinghai <yinghai.lu@...cle.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Myron Stowe <myron.stowe@...com>
Subject: Re: [Patch 1/1] x86 pci: Add option to not assign BAR's if not already
 assigned

On 05/14/2010 04:28 PM, Jesse Barnes wrote:
> On Fri, 14 May 2010 16:20:45 -0700
> "H. Peter Anvin" <hpa@...or.com> wrote:
> 
>> On 05/14/2010 03:47 PM, Jesse Barnes wrote:
>>>
>>> Wow and they're using cards that want to use I/O space?  Funky.  It's
>>> too late to get this into 2.6.34, but that can't be what you were
>>> expecting... I don't see a problem with getting something like this in
>>> for 2.6.35.
>>>
>>
>> Most cards on the market provide I/O BARs as a convenience to legacy
>> BIOSes; they don't need the I/O BAR functionality from inside a
>> full-featured OS.  There are a few, key, exceptions, mainly in the form
>> of legacy-interface devices like UARTs and VGA (note that VGA has its
>> own routing bits and is therefore unaffected by this problem.)
> 
> Yeah, it's the "legacy" part that I'm questioning.  I'm just lamenting
> that it's dying off so slowly...
> 
> And yes, VGA is an unfortunate standard.
> 

I'm not lamenting that fact, because my experience is that what ends up
replacing it is often far worse.  Consider UARTs -- no MMU dependencies
at all, can be accessed with four lines of assembly, and compare it to
EHCI debug port, the driver for which is over 900 lines in the Linux
kernel -- and that assumes that you're already in flat mode.

	-hpa
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