linux-kernel - Re[2]: pci_fixup_video change blows up on sparc64

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Message-ID: <XNM1$9$0$4$$3$3$7$A$9002706U45374cd7@hitachi.com>
Date:	Thu, 19 Oct 2006 19:01:06 +0900
From:	<eiichiro.oiwa.nm@...achi.com>
To:	"David Miller" <davem@...emloft.net>
Cc:	<alan@...hat.com>, <jesse.barnes@...el.com>, <greg@...ah.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re[2]: pci_fixup_video change blows up on sparc64

>> If an expansion ROM exists on ATI Radeon or ATY128 card, pci_map_rom returns
>> the expansion ROM base address instead of 0xC0000 because fixup_video checks
>> the VGA Enable bit in the Bridge Control register.
>
>It is not valid to expect the bridge control register to return
>anything meaningful on PCI "host bridge".  The Radeon card here sits
>on the root, just under the PCI Host Controller.  The code in
>fixup_video appears to assume that every bus up to the root from
>the VGA device is a PCI-PCI bridge, which is not a valid assumption.
>There can be a PCI host bridge at the root.

Have you ever read the PCI-to-PCI Bridge Architecture Specification?
The default of VGA Enable bit is 0. This mean video ROM doesn't forward
system RAM at 0xC0000. 

There is your VGA card under 0001:00:00.0 Host bridge. The VGA Enable bit
in this host bridge will return 0 and IORESOURCE_ROM_SHADOW won't set.

>Also, and more importantly, you cannot use the 0xc0000 address in a
>raw way like this.  There are multiple PCI domains possible in a
>given system, and the 0xc0000 address you wish to use must be relative
>to that PCI domain.
>
>Therefore, in the presence of multiple PCI domains:
>
>	x = ioremap(0xc0000, ...);
>
>doesn't make any sense, is extremely non-portable, and will crash
>on many non-x86 systems.

It's impossible that multiple VGA cards, which have not the expansion
ROM, exist in a system regardless of multiple PCI domain system.

>All of this pci_fixup_video code was perfectly fine when it was only
>used on x86, where assumptions like this happened to work, but it is
>not possible to continue making these assumptions if this code will
>now run on every single architecture.

pci_fixup_video is also perfectly fine on IA64. And VGA is historical
device of x86 platform.
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