linux-kernel - Re: [PATCH v3 05/24] arch: introduce memremap()

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Date:	Thu, 30 Jul 2015 23:02:04 +0200
From:	"Luis R. Rodriguez" <mcgrof@...e.com>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	tglx@...utronix.de, mingo@...nel.org, hpa@...or.com,
	linux-arch@...r.kernel.org, toshi.kani@...com,
	Arnd Bergmann <arnd@...db.de>, linux-nvdimm@...ts.01.org,
	linux-kernel@...r.kernel.org, rmk+kernel@....linux.org.uk,
	hch@....de, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 05/24] arch: introduce memremap()

On Thu, Jul 30, 2015 at 12:54:07PM -0400, Dan Williams wrote:
> diff --git a/include/linux/io.h b/include/linux/io.h
> index fb5a99800e77..3fcf6256c088 100644
> --- a/include/linux/io.h
> +++ b/include/linux/io.h
> @@ -121,4 +121,13 @@ static inline int arch_phys_wc_index(int handle)
>  #endif
>  #endif
>  
> +enum {
> +	/* See memremap() kernel-doc for usage description... */
> +	MEMREMAP_WB = 1 << 0,
> +	MEMREMAP_WT = 1 << 1,
> +};

Same feedback for enum nameing and also kdoc style.

> diff --git a/kernel/memremap.c b/kernel/memremap.c
> new file mode 100644
> index 000000000000..27637f42f30d
> --- /dev/null
> +++ b/kernel/memremap.c

<-- ... -->

> +/**
> + * memremap() - remap an iomem_resource as cacheable memory
> + * @offset: iomem resource start address
> + * @size: size of remap
> + * @flags: either MEMREMAP_WB or MEMREMAP_WT
> + *
> + * 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.
> + *
> + * MEMREMAP_WB - matches the default mapping for "System RAM" on
> + * the architecture.  This is usually a read-allocate write-back cache.
> + * Morever, if MEMREMAP_WB is specified and the requested remap region is RAM
> + * memremap() will bypass establishing a new mapping and instead return
> + * a pointer into the direct map.
> + *
> + * MEMREMAP_WT - establish a mapping whereby writes either bypass the
> + * cache or are written through to memory and never exist in a
> + * cache-dirty state with respect to program visibility.  Attempts to
> + * map "System RAM" with this mapping type will fail.

Then you can extrend all this on kdoc on the enum.

> + */
> +void *memremap(resource_size_t offset, size_t size, unsigned long flags)
> +{
> +	int is_ram = region_intersects(offset, size, "System RAM");

This could be the enum region_intersect_type, then if the region enum is
extended you'd get a compiler error if one type was not handled.

  Luis
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