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

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Date:	Wed, 7 Apr 2010 17:05:06 -0600
From:	Bjorn Helgaas <bjorn.helgaas@...com>
To:	Yinghai <yinghai.lu@...cle.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, linux-pci@...r.kernel.org,
	x86@...nel.org, linux-kernel@...r.kernel.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 Wednesday 07 April 2010 04:45:30 pm Yinghai wrote:
> On 04/07/2010 02:06 PM, Bjorn Helgaas wrote:
> > 
> > Currently, we only reserve the legacy VGA area [mem 0xa0000-0xbffff] on
> > x86_32.  But this legacy area is also used on x86_64, so this patch
> > reserves it there, too.
> > 
> > If we don't reserve it, we may mistakenly move a PCI device to that area,
> > as we did here:
> > 
> >   pci_root PNP0A03:00: host bridge window [mem 0xff980800-0xff980bff]
> >   pci_root PNP0A03:00: host bridge window [mem 0xff97c000-0xff97ffff]
> >   pci 0000:00:1f.2: no compatible bridge window for [mem 0xff970000-0xff9707ff]
> >   pci 0000:00:1f.2: BAR 5: assigned [mem 0x000a0000-0x000a07ff]
> > 
> > as reported by Andy Isaacson at http://lkml.org/lkml/2010/4/6/375
> > 
> > I think the fact that the BAR is not within a host bridge window is a
> > BIOS defect, and it's now more visible because we have "pci=use_crs" as
> > the default.  Using "pci=nocrs" is a workaround, because then we won't
> > attempt to move the device.
> 
> that doesn't look right.
> 
> It seem another thread, erission has one model without VGA, and they use that area for other device MMIO.
> 
> current for 64bit, We remove [0xa0000, 0x100000) from e820 map if those area is E820_RAM.
> 
> in e820_reserve_resources(), kernel will reserve range < 1M according to e820 map.
> that is before pci BAR is claimed.
> 
> or you can add
> boot_params.screen_info.orig_video_isVGA == 1
> or double check scan pci tree to see if video is there or not

I'm sorry, I can't understand what you're saying.

It seems like you're saying we already have a mechanism to keep us
from assigning that VGA range to another device, but obviously it's
not working.

Maybe it will be clearer if you propose a different patch that prevents
us from assigning 0xa0000 to the USB controller.

Bjorn
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