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

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Message-ID: <CAK8P3a0913Hs4VfHjdDY1WTAQvMzC83LJcP=9zeE0C-terfBhA@mail.gmail.com>
Date:   Wed, 24 Mar 2021 20:09:55 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Will Deacon <will@...nel.org>
Cc:     Hector Martin <marcan@...can.st>,
        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 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.

        Arnd