linux-kernel - Re: [RFC] asm-generic/pci_iomap.h: make custom PCI BAR requirements explicit

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Date:	Sat, 29 Aug 2015 08:25:05 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>
Cc:	arnd@...db.de, linux-arch@...r.kernel.org, mingo@...nel.org,
	schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
	linux-s390@...r.kernel.org, bp@...e.de, linux@...ck-us.net,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	rostedt@...dmis.org, "Luis R. Rodriguez" <mcgrof@...e.com>
Subject: Re: [RFC] asm-generic/pci_iomap.h: make custom PCI BAR requirements
 explicit

On Fri, Aug 28, 2015 at 05:17:27PM -0700, Luis R. Rodriguez wrote:
> From: "Luis R. Rodriguez" <mcgrof@...e.com>
> 
> The S390 architecture requires a custom pci_iomap() implementation
> as the asm-generic implementation assumes there are disjunctions
> between PCI BARs, and on S390 PCI BAR are not disjunctive, S390 requires
> the bar parameter in order to find the corresponding device and create
> the mapping cookie.
> 
> This clash with the asm-generic pci_iomap() implementation is implicit,
> there are no current semantics to make this incompatability explicit.
> Make the S390 PCI BAR non-disjunction incompatibility explicit, and
> also pave the way for alternative incompatibilities to be defined.
> 
> While at it, as with the ioremap*() variants, since we have no clear
> semantics yet well defined provide a solution for them that returns
> NULL. This allows architectures to move forward by defining pci_ioremap*()
> variants without requiring immediate changes to all architectures. Each
> architecture then can implement their own solution as needed and
> when they get to it.

Now that you have the config symbol available why not move the S390
implementation to generic code based on that can kill of
asm/pci_iomap.h?  Seems like we're really not dealing with something
inherent to the architecture, but two possible implementations based
on architecture constraints.
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