Re: [PATCH v2] PCI: Fix Intel i210 by avoiding overlapping of BARs

From: Michael Walle <michael@walle.cc>
To: Bjorn Helgaas <helgaas@kernel.org>
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
Date: Mon, 15 Mar 2021 22:51:25 +0100	[thread overview]
Message-ID: <d2c7ec0e416dd6bb6818892750bff6d7@walle.cc> (raw)
In-Reply-To: <20210201222010.GA31234@bjorn-Precision-5520>

Am 2021-02-01 23:20, schrieb Bjorn Helgaas:
> 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.

ping #2 ;)

-michael