From: Bjorn Helgaas <bjorn.helgaas@hp.com>
To: Jesse Barnes <jbarnes@virtuousgeek.org>
Subject: Re: fixing "pci=use_crs"
Date: Thu, 17 Sep 2009 12:57:48 -0600
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Cc: Larry Finger <Larry.Finger@lwfinger.net>, Gary Hade <garyhade@us.ibm.com>,
       Jaswinder Singh Rajput <jaswinder@kernel.org>,
       Yinghai Lu <yhlu.kernel@gmail.com>,
       Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
       Len Brown <lenb@kernel.org>,
       Linus Torvalds <torvalds@linux-foundation.org>, x86@kernel.org,
       linux-kernel@vger.kernel.org
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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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