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

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Date:	Fri, 9 Apr 2010 23:54:13 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	"H. Peter Anvin" <hpa@...or.com>
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

> 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.)

Depending on your definition of "PC". Quite a few early MSDOS systems had
video elsewhere. Some embedded systems without video use the space for
other stuff. Lots of ISA 386/486 PCs had cards borrowing the unused bits
of video space.

> 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.

Thats why you have the bios equipment byte and video queries.
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