linux-kernel - Re: [PATCH v2 02/22] asm-generic/io.h: add ioremap

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Date:   Thu, 6 Apr 2017 11:47:37 +0100
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Arnd Bergmann <arnd@...db.de>,
        Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Richard Henderson <rth@...ddle.net>,
        Tony Luck <tony.luck@...el.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Haavard Skinnemoen <hskinnemoen@...il.com>,
        Pratyush Anand <pratyush.anand@...il.com>,
        Jingoo Han <jingoohan1@...il.com>,
        Mingkai Hu <mingkai.hu@...escale.com>,
        John Garry <john.garry@...wei.com>,
        Tanmay Inamdar <tinamdar@....com>,
        Murali Karicheri <m-karicheri2@...com>,
        Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>,
        Ray Jui <rjui@...adcom.com>,
        Wenrui Li <wenrui.li@...k-chips.com>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Minghuan Lian <minghuan.Lian@...escale.com>,
        Jon Mason <jonmason@...adcom.com>,
        Gabriele Paoloni <gabriele.paoloni@...wei.com>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Michal Simek <michal.simek@...inx.com>,
        Stanimir Varbanov <svarbanov@...sol.com>,
        Zhou Wang <wangzhou1@...ilicon.com>,
        Roy Zang <tie-fei.zang@...escale.com>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>
Subject: Re: [PATCH v2 02/22] asm-generic/io.h: add ioremap_nopost remap
 interface

On Thu, Apr 06, 2017 at 11:26:36AM +0100, Lorenzo Pieralisi wrote:
> On Wed, Apr 05, 2017 at 01:38:12PM +0100, Lorenzo Pieralisi wrote:
> > eg: openrisc
> > 
> > >> include/asm-generic/io.h:922:9: error: implicit declaration of
> > >> function 'ioremap_nocache' [-Werror=implicit-function-declaration]
> >      return ioremap_nocache(offset, size);
> 
> Indeed, the static inline ioremap_nocache() fallback does not work
> on all arches (whether I add the fallback in linux/io.h or
> asm-generic/io.h is irrelevant), I bump into issues such as the one
> reported above.

>From what I can see:

(a) openrisc does define ioremap_nocache() in its asm/io.h
(b) these do not:

$ grep -L 'ioremap_nocache' arch/*/include/asm/io.h
arch/blackfin/include/asm/io.h
arch/h8300/include/asm/io.h
arch/m68k/include/asm/io.h
arch/score/include/asm/io.h
arch/sparc/include/asm/io.h

Out of those, blackfin, h8300 and score do not define it, whereas m68k
and sparc do in other headers included by asm/io.h.  So it looks like
we have three problem architectures that don't define an ioremap_nocache().

PCI on blackfin depends on BROKEN, so it's not selectable.  From what I
can tell, h8300 and score do not allow PCI to be enabled (but maybe its
buried elsewhere in their Kconfig files, I didn't check.)

So, I think a way around this is to make ioremap_nopost() conditional
on PCI in linux/io.h for the time being - if its scope wants to be
enlarged, then these three architectures would need to have either an
ioremap_nopost() implementation added, or an ioremap_nocache()
implementation.

> I could make it:
> 
> #ifndef ioremap_nopost
> static inline void __iomem *ioremap_nopost(resource_size_t offset,
> 					   unsigned long size)
> {
> 	return NULL;
> }
> #endif
> 
> which would force arches to define ioremap_nopost() (if they need it).
> 
> This is what I *assume* was done for ioremap_uc() in asm-generic/io.h,
> but honestly history is hard to follow here.

If we are going to consider doing that, the correct question we need to be
asking is whether anything will break as a result of this - is there any
existing arch using the code as it stands that will end up being broken
when we switch PCI to use ioremap_nopost(), and we end up using this NULL-
returning default?

-- 
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