linux-kernel - Re: [PATCH 2/3] PCI: Add quirks for devices found on Cavium ThunderX SoCs.

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Date:	Tue, 22 Sep 2015 08:19:16 -0500
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	David Daney <ddaney@...iumnetworks.com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	linux-arm-kernel@...ts.infradead.org,
	David Daney <ddaney.cavm@...il.com>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	Will Deacon <will.deacon@....com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>, devicetree@...r.kernel.org,
	Marc Zyngier <marc.zyngier@....com>,
	David Daney <david.daney@...ium.com>
Subject: Re: [PATCH 2/3] PCI: Add quirks for devices found on Cavium ThunderX
 SoCs.

Hi David,

On Fri, Sep 18, 2015 at 06:00:28PM -0700, David Daney wrote:
> On 09/18/2015 12:45 PM, Arnd Bergmann wrote:
> >On Friday 18 September 2015 10:00:32 David Daney wrote:
> >>On 09/18/2015 12:19 AM, Arnd Bergmann wrote:
> >>>On Thursday 17 September 2015 15:41:33 David Daney wrote:
> >>>>From: David Daney <david.daney@...ium.com>
> >>>>
> >>>>The on-chip devices all have fixed bars.  So, fix them up.
> >>>>
> >>>>Signed-off-by: David Daney <david.daney@...ium.com>
> >>>>
> >>>
> >>>You should be able to just mark the BARs as fixed in DT
> 
> I think we can switch to PCI_PROBE_ONLY, and have all non-fixed BAR
> devices configured by firmware.  This may significantly simplify any
> quirks required in the kernel.

I don't like PCI_PROBE_ONLY, and I'd like to avoid it when we can.

Your original patch description said the on-chip devices have "fixed
BARs."  In what sense are they "fixed"?  I assume they are writable
enough so we can learn their sizes?  If we can't learn their sizes, we
have bigger problems because we can't tell what space is used.

Are there other parts of the system, e.g., run-time firmware, that
depend on the devices not being moved?

> >>For the record:  The PCI Enhanced Allocation (EA) capability (approved
> >>by PCI SIG on 23 October 2014) is the proper way to handle this going
> >>forward.  However, this is not yet implemented in the SoCs that this
> >>patch addresses.  Our plan is to implement the EA capability in the core
> >>PCI code, so that we do not need to keep adding devices to this fixup code.

Sean Stalley has posted some patches to add EA support to Linux, but I
haven't merged them yet.  If we had that, another option would be to
hook into your config accessors and fabricate an EA capability.

Bjorn
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