linux-kernel - Re: [RFT PATCH v3 08/27] asm-generic/io.h: Add a non-posted variant of ioremap()

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Date:   Thu, 25 Mar 2021 14:49:06 +0000
From:   Will Deacon <will@...nel.org>
To:     Hector Martin <marcan@...can.st>
Cc:     Arnd Bergmann <arnd@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Marc Zyngier <maz@...nel.org>, Rob Herring <robh@...nel.org>,
        Olof Johansson <olof@...om.net>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Mark Kettenis <mark.kettenis@...all.nl>,
        Tony Lindgren <tony@...mide.com>,
        Mohamed Mediouni <mohamed.mediouni@...amail.com>,
        Stan Skowronek <stan@...ellium.com>,
        Alexander Graf <graf@...zon.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan Corbet <corbet@....net>,
        Catalin Marinas <catalin.marinas@....com>,
        Christoph Hellwig <hch@...radead.org>,
        "David S. Miller" <davem@...emloft.net>,
        DTML <devicetree@...r.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        "moderated list:ARM/SAMSUNG EXYNOS ARM ARCHITECTURES" 
        <linux-samsung-soc@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFT PATCH v3 08/27] asm-generic/io.h: Add a non-posted variant
 of ioremap()

On Thu, Mar 25, 2021 at 11:07:40PM +0900, Hector Martin wrote:
> On 25/03/2021 04.09, Arnd Bergmann wrote:
> > On Wed, Mar 24, 2021 at 7:12 PM Will Deacon <will@...nel.org> wrote:
> > > 
> > > > +/*
> > > > + * ioremap_np needs an explicit architecture implementation, as it
> > > > + * requests stronger semantics than regular ioremap(). Portable drivers
> > > > + * should instead use one of the higher-level abstractions, like
> > > > + * devm_ioremap_resource(), to choose the correct variant for any given
> > > > + * device and bus. Portable drivers with a good reason to want non-posted
> > > > + * write semantics should always provide an ioremap() fallback in case
> > > > + * ioremap_np() is not available.
> > > > + */
> > > > +#ifndef ioremap_np
> > > > +#define ioremap_np ioremap_np
> > > > +static inline void __iomem *ioremap_np(phys_addr_t offset, size_t size)
> > > > +{
> > > > +     return NULL;
> > > > +}
> > > > +#endif
> > > 
> > > Can we implement the generic pci_remap_cfgspace() in terms of ioremap_np()
> > > if it is supported by the architecture? That way, we could avoid defining
> > > both on arm64.
> > 
> > Good idea. It needs a fallback in case the ioremap_np() fails on most
> > architectures, but that sounds easy enough.
> > 
> > Since pci_remap_cfgspace() only has custom implementations, it sounds like
> > we can actually make the generic implementation unconditional in the end,
> > but that requires adding ioremap_np() on 32-bit as well, and I would keep
> > that separate from this series.
> 
> Sounds good; I'm adding a patch to adjust the generic implementation and
> remove the arm64 one in v4, and we can then complete the cleanup for other
> arches later.

Cheers. Don't forget to update the comment in the generic code which
complains about the lack of an ioremap() API for non-posted writes ;)

Will