linux-kernel - Re: [PATCH v5 2/6] arch: unify ioremap prototypes and macro aliases

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Date:	Wed, 1 Jul 2015 08:23:52 +0200
From:	Christoph Hellwig <hch@....de>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	Christoph Hellwig <hch@....de>, Arnd Bergmann <arnd@...db.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Juergen Gross <jgross@...e.com>, X86 ML <x86@...nel.org>,
	"Kani, Toshimitsu" <toshi.kani@...com>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Luis Rodriguez <mcgrof@...e.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Stefan Bader <stefan.bader@...onical.com>,
	Andy Lutomirski <luto@...capital.net>, linux-mm@...ck.org,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	mpe@...erman.id.au, Tejun Heo <tj@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v5 2/6] arch: unify ioremap prototypes and macro aliases

On Tue, Jun 30, 2015 at 03:57:16PM -0700, Dan Williams wrote:
> > void __iomem *ioremap_flags(resource_size_t offset, unsigned long size,
> >                         unsigned long prot_val, unsigned flags);
> 
> Doesn't 'flags' imply a specific 'prot_val'?

Looks like the values are arch specific.  So as a first step I'd like
to keep them separate.  As a second step we could look into unifying
the actual ioremap implementations which look mostly the same.  Once
that is done we could look into collapsing the flags and prot_val
arguments.

> One useful feature of the ifdef mess as implemented in the patch is
> that you could test for whether ioremap_cache() is actually
> implemented or falls back to default ioremap().  I think for
> completeness archs should publish an ioremap type capabilities mask
> for drivers that care... (I can imagine pmem caring), or default to
> being permissive if something like IOREMAP_STRICT is not set.  There's
> also the wrinkle of archs that can only support certain types of
> mappings at a given alignment.

I think doing this at runtime might be a better idea.  E.g. a
ioremap_flags with the CACHED argument will return -EOPNOTSUP unless
actually implemented.  On various architectures different CPUs or
boards will have different capabilities in this area.
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