linux-kernel - Re: [PATCH v3 5/6] arch: introduce memremap_cache() and memremap

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Date:	Mon, 8 Jun 2015 19:27:12 +0300
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	Arnd Bergmann <arnd@...db.de>, Ingo Molnar <mingo@...hat.com>,
	bp@...en8.de, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	ross.zwisler@...ux.intel.com,
	Andrew Morton <akpm@...ux-foundation.org>, jgross@...e.com,
	"x86@...nel.org" <x86@...nel.org>, toshi.kani@...com,
	linux-nvdimm@...ts.01.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	mcgrof@...e.com, konrad.wilk@...cle.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	stefan.bader@...onical.com, luto@...capital.net,
	linux-mm@...ck.org, Geert Uytterhoeven <geert@...ux-m68k.org>,
	Ralf Baechle <ralf@...ux-mips.org>, hmh@....eng.br,
	mpe@...erman.id.au, Tejun Heo <tj@...nel.org>, paulus@...ba.org,
	hch@....de
Subject: Re: [PATCH v3 5/6] arch: introduce memremap_cache() and memremap_wt()

On Thu, Jun 4, 2015 at 12:34 AM, Dan Williams <dan.j.williams@...el.com> wrote:
> Existing users of ioremap_cache() are mapping memory that is known in
> advance to not have i/o side effects.  These users are forced to cast
> away the __iomem annotation, or otherwise neglect to fix the sparse
> errors thrown when dereferencing pointers to this memory.  Provide
> memremap_*() as a non __iomem annotated ioremap_*().
>
> The ARCH_HAS_MEMREMAP kconfig symbol is introduced for archs to assert
> that it is safe to recast / reuse the return value from ioremap as a
> normal pointer to memory.  In other words, archs that mandate specific
> accessors for __iomem are not memremap() capable and drivers that care,
> like pmem, can add a dependency to disable themselves on these archs.

One minor comment. Otherwise looks good for me.

[]

> --- a/kernel/resource.c
> +++ b/kernel/resource.c

> @@ -528,6 +528,45 @@ int region_is_ram(resource_size_t start, unsigned long size)
>         return ret;
>  }
>
> +#ifdef CONFIG_ARCH_HAS_MEMREMAP
> +/*
> + * memremap() is "ioremap" for cases where it is known that the resource
> + * being mapped does not have i/o side effects and the __iomem
> + * annotation is not applicable.
> + */
> +static bool memremap_valid(resource_size_t offset, size_t size)
> +{
> +       if (region_is_ram(offset, size) != 0) {
> +               WARN_ONCE(1, "memremap attempted on ram %pa size: %zd\n",

%zu

> +                               &offset, size);
> +               return false;
> +       }
> +       return true;
> +}


-- 
With Best Regards,
Andy Shevchenko
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