linux-kernel - Re: [PATCH v2 08/25] arch: introduce memremap()

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Message-ID: <20150729182712.GI30479@wotan.suse.de>
Date:	Wed, 29 Jul 2015 20:27:13 +0200
From:	"Luis R. Rodriguez" <mcgrof@...e.com>
To:	Christoph Hellwig <hch@....de>
Cc:	Dan Williams <dan.j.williams@...el.com>,
	linux-arch@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 08/25] arch: introduce memremap()

On Wed, Jul 29, 2015 at 08:50:04AM +0200, Christoph Hellwig wrote:
> On Mon, Jul 27, 2015 at 04:26:03PM -0700, Dan Williams wrote:
> > Oh, because all we have at this point is ioremap_cache() which
> > silently falls back.  It's not until the introduction of
> > arch_memremp() where we update the arch code to break that behavior.
> 
> Ok, makes sense.  Might be worth to document in the changelog.
> 
> > That said, I think it may be beneficial to allow a fallback if the
> > user cares.  So maybe memremap() can call plain ioremap() if
> > MEMREMAP_STRICT is not set and none of the other mapping types are
> > satisfied.
> 
> Is there a real use case for it?  Fallback APIs always seem confusing
> and it might make more sense to do this in the caller(s) that actually
> need it.

It seems semantics-wise we are trying to separate these two really, so I agree
with this. Having a fallback would onloy make things more complicated for any
sanitizer / checker / etc, and I don't think the practical gains of having a
fallback outweight the gains of having a clear semantic separation on intended
memory type and interactions with it.

  Luis
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