linux-kernel - Re: Please revert: PCI: fix IDE legacy mode resources

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Date:	Tue, 11 Dec 2007 12:13:43 +0000
From:	Ralf Baechle <ralf@...ux-mips.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Yoichi Yuasa <yoichi_yuasa@...peaks.co.jp>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Greg KH <gregkh@...e.de>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
Subject: Re: Please revert: PCI: fix IDE legacy mode resources

On Tue, Dec 11, 2007 at 11:27:24AM +1100, Benjamin Herrenschmidt wrote:

> > The GT-64111 system controller doesn't provide any kind of mapping
> > functionality that would help here.  So legacy port addressing can only
> > work by exploiting aliases due to incomplete decoding of legacy ioport
> > addreses by the VT82C586 - but direct addressing is impossible.
> 
> Ok, that explains how the "fix" that we reverted worked. It caused crap
> to be added to the top bits of the address :-)
> 
> So here, what you really want to do is not a call to
> pcibios_resource_to_bus(), but you actually want to use a different bus
> address in the first place, that you know the HW will decode the same
> way.
> 
> The best way to achieve that imho, is to do a header quirk that is run
> just after the generic probe code, which offsets the fixed legacy
> resources by 0x10000000 since that's really the bus address you are
> going to emit.
> 
> Later on, your pcibios_fixup code should take that remove 0x10000000
> from all IO resources, since your 0xd0000000 mapping already maps
> 0x10000000 as you probably already do.
> 
> The trick is, you don't want to convert a "resource" into a "bus
> address" here, but really issue a different bus address.

Oh well, I've cooked up a patch and posted it to linux-mips for testing.

  Ralf
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