From mboxrd@z Thu Jan  1 00:00:00 1970
From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Subject: Re: [PATCH v3 04/32] asm-generic: add ioremap_nopost() remap interface
Date: Wed, 12 Apr 2017 11:00:28 +0100
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To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Jonas Bonn <jonas@southpole.se>, Rich Felker <dalias@libc.org>, linux-pci@vger.kernel.org, Will Deacon <will.deacon@arm.com>, "James E.J. Bottomley" <jejb@parisc-linux.org>, David Howells <dhowells@redhat.com>, Max Filippov <jcmvbkbc@gmail.com>, Paul Mackerras <paulus@samba.org>, Huacai Chen <chenhc@lemote.com>, Guan Xuetao <gxt@mprc.pku.edu.cn>, Thomas Gleixner <tglx@linutronix.de>, Hans-Christian Egtvedt <egtvedt@samfundet.no>, linux-arch@vger.kernel.org, Jesper Nilsson <jesper.nilsson@axis.com>, Yoshinori Sato <ysato@users.sourceforge.jp>, Michael Ellerman <mpe@ellerman.id.au>, Helge Deller <deller@gmx.de>, Russell King <linux@armlinux.org.uk>, Ingo Molnar <mingo@redhat.com>, Geert Uytterhoeven <geert@linux-m68k.org>, Catalin Marinas <catalin.marinas@arm.com>, Matt Turner <mattst88@gmail.com>, Haavard Skinnemoen <hskinnemoen@gmail.com>, Fenghua Yu <fenghua.yu@intel.co>
List-Id: linux-arch.vger.kernel.org

On Wed, Apr 12, 2017 at 09:14:07AM +1000, Benjamin Herrenschmidt wrote:
> On Tue, 2017-04-11 at 15:31 +0100, Lorenzo Pieralisi wrote:
> > > This is a semantic that simply *cannot* be generically provided accross
> > > architectures as a mapping attribute.
> > 
> > I agree that a default implementation does not make much sense. The
> > only solution to this, if we want the ioremap_nopost to be made available
> > to generic code (and drivers - ie DT PCI host bridge drivers on ARM/ARM64
> > are not arch code), is to make the ioremap_nopost() call return NULL
> > unless overriden by arch code that can provide its semantics.
> 
> That would be a better option.

I think that's what I will implement which basically means I will
replace the default:

static inline void __iomem *ioremap_nopost(phys_addr_t offset, size_t size)
{
	return ioremap_nocache(offset, size);
}

with

static inline void __iomem *ioremap_nopost(phys_addr_t offset, size_t size)
{
	return NULL;
}

If an arch can override ioremap_nopost() with sensible mapping
attributes (or whatever make it enforceable) it does, if it can't
any ioremap_nopost() usage will result in a mapping failure, if you
see any other viable solution please shout.

Thanks,
Lorenzo