linux-kernel - Re: [RFT PATCH v3 12/27] of/address: Add infrastructure to declare MMIO as non-posted

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Date:   Fri, 5 Mar 2021 11:28:37 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Hector Martin <marcan@...can.st>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Marc Zyngier <maz@...nel.org>, Rob Herring <robh@...nel.org>,
        Arnd Bergmann <arnd@...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>,
        Will Deacon <will@...nel.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>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFT PATCH v3 12/27] of/address: Add infrastructure to declare
 MMIO as non-posted

On Thu, Mar 4, 2021 at 10:40 PM Hector Martin <marcan@...can.st> wrote:

> This implements the 'nonposted-mmio' and 'posted-mmio' boolean
> properties. Placing these properties in a bus marks all child devices as
> requiring non-posted or posted MMIO mappings. If no such properties are
> found, the default is posted MMIO.
>
> of_mmio_is_nonposted() performs the tree walking to determine if a given
> device has requested non-posted MMIO.
>
> of_address_to_resource() uses this to set the IORESOURCE_MEM_NONPOSTED
> flag on resources that require non-posted MMIO.
>
> of_iomap() and of_io_request_and_map() then use this flag to pick the
> correct ioremap() variant.
>
> This mechanism is currently restricted to Apple ARM platforms, as an
> optimization.
>
> Signed-off-by: Hector Martin <marcan@...can.st>

This is fine with me atleast given that the nonposted IO is acceptable.
Caching the quirk state in a static local is maybe a bit overoptimized
but if the compiler can't see it but we can, why not.
Reviewed-by: Linus Walleij <linus.walleij@...aro.org>

Yours,
Linus Walleij