linux-kernel - Re: [PATCH v7 1/6] pci: Introduce pci_register_io

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Date:	Tue, 8 Apr 2014 10:54:01 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Liviu Dudau <Liviu.Dudau@....com>,
	linux-pci <linux-pci@...r.kernel.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linaro-kernel <linaro-kernel@...ts.linaro.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	LAKML <linux-arm-kernel@...ts.infradead.org>,
	Tanmay Inamdar <tinamdar@....com>,
	Grant Likely <grant.likely@...retlab.ca>
Subject: Re: [PATCH v7 1/6] pci: Introduce pci_register_io_range() helper function.

On Tue, Apr 8, 2014 at 4:22 AM, Arnd Bergmann <arnd@...db.de> wrote:
> On Tuesday 08 April 2014 10:50:39 Liviu Dudau wrote:
>> On Mon, Apr 07, 2014 at 06:58:24PM +0100, Bjorn Helgaas wrote:
>> > On Mon, Apr 7, 2014 at 5:36 AM, Arnd Bergmann <arnd@...db.de> wrote:
>> >
>> > > I think migrating other architectures to use the same code should be
>> > > a separate effort from adding a generic implementation that can be
>> > > used by arm64. It's probably a good idea to have patches to convert
>> > > arm32 and/or microblaze.
>> >
>> > Let me reiterate that I am 100% in favor of replacing arch-specific
>> > code with more generic implementations.
>> >
>> > However, I am not 100% in favor of doing it as separate efforts
>> > (although maybe I could be convinced).  The reasons I hesitate are
>> > that (1) if only one architecture uses a new "generic" implementation,
>> > we really don't know whether it is generic enough, (2) until I see the
>> > patches to convert other architectures, I have to assume that I'm the
>> > one who will write them, and (3) as soon as we add the code to
>> > drivers/pci, it becomes partly my headache to maintain it, even if
>> > only one arch benefits from it.
>
> Fair enough.
>
> My approach to the asm-generic infrastruction has mostly been to ensure
> that whoever adds a new architecture has to make things easier for the
> next person.

That's a good rule.  But if we add a generic implementation used only
by one architecture, the overall complexity has increased (we added
new unshared code), so the next person has to look at N+1 existing
implementations.  If we even convert one existing arch, that seems
like an improvement: we have N implementations with one being used by
at least two arches.

Bjorn
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