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Date:   Mon, 1 Feb 2021 16:20:10 -0600
From:   Bjorn Helgaas <helgaas@kernel.org>
To:     Michael Walle <michael@walle.cc>
Cc:     linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
        intel-wired-lan@lists.osuosl.org,
        Bjorn Helgaas <bhelgaas@google.com>,
        Jesse Brandeburg <jesse.brandeburg@intel.com>,
        Tony Nguyen <anthony.l.nguyen@intel.com>,
        Paul Menzel <pmenzel@molgen.mpg.de>
Subject: Re: [PATCH v2] PCI: Fix Intel i210 by avoiding overlapping of BARs
Message-ID: <20210201222010.GA31234@bjorn-Precision-5520>
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On Mon, Feb 01, 2021 at 08:49:16PM +0100, Michael Walle wrote:
> Am 2021-01-17 20:27, schrieb Michael Walle:
> > Am 2021-01-16 00:57, schrieb Bjorn Helgaas:
> > > On Wed, Jan 13, 2021 at 12:32:32AM +0100, Michael Walle wrote:
> > > > Am 2021-01-12 23:58, schrieb Bjorn Helgaas:
> > > > > On Sat, Jan 09, 2021 at 07:31:46PM +0100, Michael Walle wrote:
> > > > > > Am 2021-01-08 22:20, schrieb Bjorn Helgaas:
> > > 
> > > > > > > 3) If the Intel i210 is defective in how it handles an Expansion ROM
> > > > > > > that overlaps another BAR, a quirk might be the right fix. But my
> > > > > > > guess is the device is working correctly per spec and there's
> > > > > > > something wrong in how firmware/Linux is assigning things.  That would
> > > > > > > mean we need a more generic fix that's not a quirk and not tied to the
> > > > > > > Intel i210.
> > > > > >
> > > > > > Agreed, but as you already stated (and I've also found that in
> > > > > > the PCI spec) the Expansion ROM address decoder can be shared by
> > > > > > the other BARs and it shouldn't matter as long as the ExpROM BAR
> > > > > > is disabled, which is the case here.
> > > > >
> > > > > My point is just that if this could theoretically affect devices
> > > > > other than the i210, the fix should not be an i210-specific quirk.
> > > > > I'll assume this is a general problem and wait for a generic PCI
> > > > > core solution unless it's i210-specific.
> > > > 
> > > > I guess the culprit here is that linux skips the programming of the
> > > > BAR because of some broken Matrox card. That should have been a
> > > > quirk instead, right? But I don't know if we want to change that, do
> > > > we? How many other cards depend on that?
> > > 
> > > Oh, right.  There's definitely some complicated history there that
> > > makes me a little scared to change things.  But it's also unfortunate
> > > if we have to pile quirks on top of quirks.
> > > 
> > > > And still, how do we find out that the i210 is behaving correctly?
> > > > In my opinion it is clearly not. You can change the ExpROM BAR value
> > > > during runtime and it will start working (while keeping it
> > > > disabled).  Am I missing something here?
> > > 
> > > I agree; if the ROM BAR is disabled, I don't think it should matter at
> > > all what it contains, so this does look like an i210 defect.
> > > 
> > > Would you mind trying the patch below?  It should update the ROM BAR
> > > value even when it is disabled.  With the current pci_enable_rom()
> > > code that doesn't rely on the value read from the BAR, I *think* this
> > > should be safe even on the Matrox and similar devices.
> > 
> > Your patch will fix my issue:
> > 
> > Tested-by: Michael Walle <michael@walle.cc>
> 
> any news on this?

Thanks for the reminder.  I was thinking this morning that I need to
get back to this.  I'm trying to convince myself that doing this
wouldn't break the problem fixed by 755528c860b0 ("Ignore disabled ROM
resources at setup").  So far I haven't quite succeeded.

Bjorn