linux-kernel - Re: [PATCH v8 3/6] pci:host: Add Altera PCIe host controller driver

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Date:	Mon, 12 Oct 2015 14:03:04 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Bjorn Helgaas <helgaas@...nel.org>
Cc:	Ley Foon Tan <lftan@...era.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Marc Zyngier <marc.zyngier@....com>,
	Dinh Nguyen <dinguyen@...nsource.altera.com>,
	linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	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>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Subject: Re: [PATCH v8 3/6] pci:host: Add Altera PCIe host controller driver

On Friday 09 October 2015 18:15:40 Bjorn Helgaas wrote:
> 
> I don't know if this should be a kernel taint, a simple warning in
> dmesg, or what.  I guess the tainting mechanism is probably too
> general-purpose for this, and add_taint() doesn't give any dmesg
> indication.  We wouldn't see the taint unless the problem actually
> caused an oops or panic.  In this case, I think I want a clue in dmesg
> so we have a chance of seeing it even if there is no oops.  So
> probably something like a dev_warn("non-compliant config accesses")
> would work.
> 
> You really should double-check with the hardware guys, because it's
> pretty obvious that the PCI spec requires 1- and 2-byte config
> accesses to work correctly.  For example, if you read/modify/write to
> update PCI_COMMAND, you will inadvertently clear the RW1C bits in
> PCI_STATUS.

Would it help to require a DT property here that flags the device
as having a broken config space?

Then we could implement both in the driver, and only use the
RMW based implementation if the firmware describes the device
as "altera,broken-pci-config-space".

	Arnd
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