linux-kernel - Re: [RFT PATCH v3 11/27] arm64: Implement ioremap

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Message-ID: <20210324181803.GD13181@willie-the-truck>
Date:   Wed, 24 Mar 2021 18:18:04 +0000
From:   Will Deacon <will@...nel.org>
To:     Hector Martin <marcan@...can.st>
Cc:     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>,
        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>,
        devicetree@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFT PATCH v3 11/27] arm64: Implement ioremap_np() to map MMIO
 as nGnRnE

On Fri, Mar 05, 2021 at 06:38:46AM +0900, Hector Martin wrote:
> This is used on Apple ARM platforms, which require most MMIO
> (except PCI devices) to be mapped as nGnRnE.
> 
> Signed-off-by: Hector Martin <marcan@...can.st>
> ---
>  arch/arm64/include/asm/io.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm64/include/asm/io.h b/arch/arm64/include/asm/io.h
> index 5ea8656a2030..953b8703af60 100644
> --- a/arch/arm64/include/asm/io.h
> +++ b/arch/arm64/include/asm/io.h
> @@ -169,6 +169,7 @@ extern void __iomem *ioremap_cache(phys_addr_t phys_addr, size_t size);
>  
>  #define ioremap(addr, size)		__ioremap((addr), (size), __pgprot(PROT_DEVICE_nGnRE))
>  #define ioremap_wc(addr, size)		__ioremap((addr), (size), __pgprot(PROT_NORMAL_NC))
> +#define ioremap_np(addr, size)		__ioremap((addr), (size), __pgprot(PROT_DEVICE_nGnRnE))

Probably worth noting that whether or not this actually results in a
non-posted mapping depends on the system architecture, but this is the
best we can do, so:

Acked-by: Will Deacon <will@...nel.org>

I would personally prefer that drivers didn't have to care about this, and
ioremap on arm64 figured out the right attributes based on the region being
mapped, but I haven't followed the discussion closely so I won't die on that
hill.

Will