linux-kernel - Re: [PATCH v6 6/6] pci: Add support for creating a generic host

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Date:	Mon, 10 Mar 2014 16:21:01 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Liviu Dudau <Liviu.Dudau@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	linaro-kernel <linaro-kernel@...ts.linaro.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	linux-pci <linux-pci@...r.kernel.org>,
	Will Deacon <Will.Deacon@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Tanmay Inamdar <tinamdar@....com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH v6 6/6] pci: Add support for creating a generic host_bridge from device tree

On Monday 10 March 2014 14:44:14 Liviu Dudau wrote:
> I will try to improve the error handling in the next patchset version.
> However I am still confused about the earlier discussion on
> pci_register_io_range(). Your suggestion initially was to return an
> error in the default weak implementation, but in your last email you
> are talking about returning 'port'.

You can do either one: 'port' should be positive or zero, while the
error would always be negative. We do the same thing in many interfaces
in the kernel.

> My idea when I've introduced the
> helper function was that it would return an error if it fails to
> register the IO range and zero otherwise. I agree that we can treat
> the default 'do nothing with the IO range' case as an error, with
> the caveat that will force architectures that use this code to
> provide their own implementation of pci_register_io_range() in order
> to avoid failure, even for the cases where the architecture has a 1:1
> mapping between IO and CPU addresses.

Which architectures are you thinking of? The only one I know that
does this is ia64, and we won't ever have to support this helper
on that architecture.

I did not ask to treat 'do nothing with the IO range' as an error,
what I meant is that we should treat 'architecture cannot translate
from I/O space to memory space but DT lists a translation anyway'
as an error. On x86, you should never see an entry for the I/O space
in "ranges", so we will not call this function unless there is a
bug in DT.

	Arnd
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