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 13:31:48 -0700
From:	Guenter Roeck <guenter.roeck@...csson.com>
To:	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
CC:	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 Fri, 2010-04-09 at 16:11 -0400, H. Peter Anvin wrote:
> On 04/09/2010 11:55 AM, Guenter Roeck wrote:
> > On Fri, 2010-04-09 at 14:23 -0400, H. Peter Anvin wrote:
> >> [Adding Guenter Roeck as he was commenting on something writing to the
> >> VGA area...]
> >>
> >> On 04/09/2010 10:22 AM, Yinghai wrote:
> >>>
> >>> then please check this one
> >>>
> >>> update e820 at first, and later put them resource tree, but give pci BAR chance to claim
> >>> the range, before assign unassigned resources.
> >>>
> >>> in case some system doesn't have VGA, and use [0xa0000, ..] for mmio of some other pci devices.
> >>>
> >>
> >> Do we have any evidence of any such system?
> >>
> >> Either which way, the patch looks saner...
> >>
> > Yes, we have a system which does not have VGA and uses the VGA memory
> > space for another device. I don't know exactly what for, but I can find
> > out if it is relevant.
> > 
> 
> Quite.  We really need to consider if that kind of devices should be
> supported.

It is used for a custom FPGA implementing a watchdog timer and some
other functionality.

This is not a matter of supporting such a device in Linux, it is a
matter of explicitly excluding non-VGA devices from using VGA memory
space.

If that is the decision, it might be worthwhile mentioning it somewhere
in the documentation, to prevent others from ever using that memory
space in an embedded system (and to save them the time needed to find
out about it and to identify and implement a workaround).

Guenter


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