linux-kernel - Re: [PATCH v8 4/9] pci: OF: Fix the conversion of IO ranges into IO resources.

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Date:	Mon, 7 Jul 2014 23:22:00 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Liviu Dudau <Liviu.Dudau@....com>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Rob Herring <robherring2@...il.com>,
	Sinan Kaya <okaya@...eaurora.org>,
	"linaro-kernel" <linaro-kernel@...ts.linaro.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Device Tree ML <devicetree@...r.kernel.org>,
	"linux-pci" <linux-pci@...r.kernel.org>,
	Jingoo Han <jg1.han@...sung.com>,
	Will Deacon <Will.Deacon@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Tanmay Inamdar <tinamdar@....com>,
	Suravee Suthikulanit <suravee.suthikulpanit@....com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH v8 4/9] pci: OF: Fix the conversion of IO ranges into IO resources.

On Monday 07 July 2014, Liviu Dudau wrote:
> On Sat, Jul 05, 2014 at 09:46:09PM +0100, Arnd Bergmann wrote:
> > On Saturday 05 July 2014 14:25:52 Rob Herring wrote:
> > > On Tue, Jul 1, 2014 at 1:43 PM, Liviu Dudau <Liviu.Dudau@....com> wrote:
> > > > The ranges property for a host bridge controller in DT describes
> > > > the mapping between the PCI bus address and the CPU physical address.
> > > > The resources framework however expects that the IO resources start
> > > > at a pseudo "port" address 0 (zero) and have a maximum size of IO_SPACE_LIMIT.
> > > > The conversion from pci ranges to resources failed to take that into account.
> > > 
> > > I don't think this change is right. There are 2 resources: the PCI bus
> > > addresses and cpu addresses. This function deals with the cpu
> > > addresses. Returning pci addresses for i/o and cpu addresses for
> > > memory is going to be error prone. We probably need both cpu and pci
> > > resources exposed to host controllers.
> > > 
> > > Making the new function only deal with i/o bus resources and naming it
> > > of_pci_range_to_io_resource would be better.
> > 
> > I think you are correct that this change by itself is will break existing
> > drivers that rely on the current behavior of of_pci_range_to_resource,
> > but there is also something wrong with the existing implementation:
> 
> Either I'm very confused or I've managed to confuse everyone else. The I/O
> resources described using CPU addresses *are* using "pseudo" port based
> addresses (or at least that is my understanding and my reading of the code).
> Can you point me to a function that is expecting the IO resource to have
> the start address at the physical address of the mapped space?

pci_v3_preinit() in arch/arm/mach-integrator/pci_v3.c for instance takes
the resource returned by of_pci_range_to_resource and programs the
start and size into hardware registers that expect a physical address
as far as I can tell.

> I was trying to fix exactly this issue, that you cannot use the resource
> structure returned by this function in any call that is expecting an IO
> resource.

I looked at the other drivers briefly, and I think you indeed fix the Tegra
driver with this but break the integrator driver as mentioned above.
The other callers of of_pci_range_to_resource() are apparently not
impacted as they recalculate the values they get.

	Arnd
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