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

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Message-Id: <200712091346.25532.bzolnier@gmail.com>
Date:	Sun, 9 Dec 2007 13:46:25 +0100
From:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
To:	benh@...nel.crashing.org
Cc:	Ralf Baechle <ralf@...ux-mips.org>,
	Yoichi Yuasa <yoichi_yuasa@...peaks.co.jp>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Greg KH <gregkh@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: Please revert: PCI: fix IDE legacy mode resources

On Sunday 09 December 2007, Benjamin Herrenschmidt wrote:
> 
> > If that is the case though (that is it can't issue low ioport cycles),
> > how would have the fd6e7321...  worked in the first place ? Hrm...
> > strange. My understanding is that all that patch does is put junk in the
> > pci_dev resource structures :-) Maybe that's enough to cause the PCI
> > layer later on to be unhappy about them and reassign the BARs to some
> > place that works ? In which case, you are right, a better approach is a
> > quirk on this specific platform, or even better, mark 0...0x10000000
> > busy in ioport_resources and let the generic code clash & re-assign...
> 
>   .../...
> 
> In fact, I see a deeper problem with Bart's original patch that moved
> the "fixup" the PCI probe.

I don't remember changing anything there, could you remind me what it was
exactly (commit number or patch name)?

> The code now replaces the content of the resource structures with the
> hard-decoded legacy addresses for any IDE controller in legacy mode,
> just losing whatever was there (the real BAR value).
> 
> On some platforms, like PowerPC (and it might be the same problem MIPS
> has, I don't know for sure), we have a quirk that puts those controller
> back into native mode. But so far, those quirks didn't change the
> resources as they were supposed to contain the proper BAR values that
> would, from then, be used.
> 
> Now that those values have been overriden in the resources, when the
> controller is switched to native mode, it will answer to the BAR values
> that no longer match the content of the resources and the driver will
> fail.
> 
> So I think we have a deeper breakage here. I'll dig some machines for
> which we do that tomorrow and see what exactly is going on. It's mostly
> older machines so if there's a breakage, it has easily gone under the
> radar.
> 
> I suspect any platform with such a quirk to turn IDE controllers into
> native mode will now -also- need to put back the BAR values in the
> struct resource, and do so -before- the platform fixup happens, that is
> from a header quirk.
> 
> Cheers,
> Ben.
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