linux-kernel - Re: fixing "pci=use

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Message-Id: <200909171257.48851.bjorn.helgaas@hp.com>
Date:	Thu, 17 Sep 2009 12:57:48 -0600
From:	Bjorn Helgaas <bjorn.helgaas@...com>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
Cc:	Larry Finger <Larry.Finger@...inger.net>,
	Gary Hade <garyhade@...ibm.com>,
	Jaswinder Singh Rajput <jaswinder@...nel.org>,
	Yinghai Lu <yhlu.kernel@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Len Brown <lenb@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: fixing "pci=use_crs"

On Thursday 17 September 2009 10:45:27 am Jesse Barnes wrote:
> > The extra resources in the old dmesg could be from "pci=use_crs"
> > being the default, but if that were the case, they should be in
> > the PNP resource dump.  Did you update the BIOS between those
> > boots?
> 
> FWIW in the CRS problem thread there were other reports of large
> numbers of PNP resources causing problems.  One solution I considered
> before we ended up reverting the patch was to increase the number of
> bus resources we track.  Rather than a small array of resources per
> bus, we could have a linked list, which would allow us to track an
> arbitrary number.

I think that might be a good starting point anyway, since I'm not
aware of any spec that limits the number of apertures a host bridge
can have.

> We probably want to distinguish between what we read from the hw regs
> and what's reported in PNP though, so maybe a new list in addition to
> the existing resource set would be the way to go.  That would allow us
> to selectively ignore PNP resources on machines where they report bogus
> ranges (or selectively look at them, either way).

When we can read things from hardware registers, I think we have to
trust that more than anything from other sources.  But I'm not proposing
any particular solution yet; I just want to get a better understanding
of what we're seeing.

Bjorn
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