linux-kernel - Re: [PATCH v1] x86/mm, asm-generic: Add IOMMU ioremap

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Message-ID: <CABhMZUVybSZPrLPWfFhCJKwk922UbacUzhzkMYNvb_++kGuPQw@mail.gmail.com>
Date:   Thu, 16 Mar 2017 15:46:51 -0500
From:   Bjorn Helgaas <bjorn.helgaas@...il.com>
To:     "Luis R. Rodriguez" <mcgrof@...not-panic.com>
Cc:     mingo@...nel.org, bp@...e.de, arnd@...db.de,
        dan.j.williams@...el.com, Christoph Hellwig <hch@....de>,
        luto@...capital.net, hpa@...or.com, tglx@...utronix.de,
        geert@...ux-m68k.org, ralf@...ux-mips.org, hmh@....eng.br,
        ross.zwisler@...ux.intel.com, akpm@...ux-foundation.org,
        jgross@...e.com, Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        mpe@...erman.id.au, tj@...nel.org, x86 <x86@...nel.org>,
        tomi.valkeinen@...com, mst@...hat.com, toshi.kani@...com,
        stefan.bader@...onical.com, linux-mm@...ck.org,
        linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Luis R. Rodriguez" <mcgrof@...e.com>
Subject: Re: [PATCH v1] x86/mm, asm-generic: Add IOMMU ioremap_uc() variant default

On Thu, Jul 9, 2015 at 7:28 PM, Luis R. Rodriguez
<mcgrof@...not-panic.com> wrote:

> +/**
> + * DOC: ioremap() and ioremap_*() variants
> + *
> + * If you have an IOMMU your architecture is expected to have both ioremap()
> + * and iounmap() implemented otherwise the asm-generic helpers will provide a
> + * direct mapping.
> + *
> + * There are ioremap_*() call variants, if you have no IOMMU we naturally will
> + * default to direct mapping for all of them, you can override these defaults.
> + * If you have an IOMMU you are highly encouraged to provide your own
> + * ioremap variant implementation as there currently is no safe architecture
> + * agnostic default. To avoid possible improper behaviour default asm-generic
> + * ioremap_*() variants all return NULL when an IOMMU is available. If you've
> + * defined your own ioremap_*() variant you must then declare your own
> + * ioremap_*() variant as defined to itself to avoid the default NULL return.

Are the references above to "IOMMU" typos?  Should they say "MMU"
instead, so they match the #ifdef below?

> + */
> +
> +#ifdef CONFIG_MMU
> +
> +#ifndef ioremap_uc
> +#define ioremap_uc ioremap_uc
> +static inline void __iomem *ioremap_uc(phys_addr_t offset, size_t size)
> +{
> +       return NULL;
> +}
> +#endif
> +
> +#else /* !CONFIG_MMU */
> +
>  /*
>   * Change "struct page" to physical address.
>   *
> @@ -743,7 +772,6 @@ static inline void *phys_to_virt(unsigned long address)
>   * you'll need to provide your own definitions.
>   */
>
> -#ifndef CONFIG_MMU
>  #ifndef ioremap
>  #define ioremap ioremap
>  static inline void __iomem *ioremap(phys_addr_t offset, size_t size)
> --
> 2.3.2.209.gd67f9d5.dirty
>
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