linux-kernel - Re: [PATCH] x86: Reserve legacy VGA MMIO area for x86_64 as well as x86

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Date:	Fri, 09 Apr 2010 15:42:17 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	guenter.roeck@...csson.com, linux-kernel@...r.kernel.org,
	Yinghai <yinghai.lu@...cle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Bjorn Helgaas <bjorn.helgaas@...com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	Andy Isaacson <adi@...apodia.org>,
	Thomas Renninger <trenn@...e.de>
Subject: Re: [PATCH] x86: Reserve legacy VGA MMIO area for x86_64 as well
 as x86_32

On 04/09/2010 03:42 PM, Alan Cox wrote:
>> "Don't use legacy fixed-function addresses for nonstandard purposes."
>>
>> There, there is your documentation.
> 
> It's probably a good idea to only reserve it if the space is actually
> being used. There are a variety of legitimate reasons to use that space
> for other things on embedded x86 boards.
> 
> They are only "legacy fixed function" if you have a PCI bus...

No they're not.  The 0xa0000...0xbffff range has been a legacy video
area since the very first PC (although the first PC only used
0xb0000..0xbffff, 0xa0000..0xbffff was declared reserved at that time.)

I'm wondering what those legitimate reasons are.  This is particularly
so since it affects our ability to deal with very early errors, long
before we have enumerated anything.  At this point we can at least lay
down bytes in the video area and hope the user can see them.

	-hpa

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