linux-kernel - Re: [PATCH v2 1/4] ARM: new cache maintenance api for iommu mem flush

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Date:	Wed, 20 Jun 2012 09:43:30 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	"Gupta, Ramesh" <grgupta@...com>
Cc:	linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, tony@...mide.com
Subject: Re: [PATCH v2 1/4] ARM: new cache maintenance api for iommu mem
	flush

On Tue, Jun 19, 2012 at 04:51:07PM +0530, Gupta, Ramesh wrote:
> >From 785a1f2854002ce7c1c8880bc5d8d92a7868bf1c Mon Sep 17 00:00:00 2001
> From: Ramesh Gupta G <grgupta@...com>
> Date: Fri, 15 Jun 2012 16:37:20 +0530
> Subject: [PATCH v2 1/4] ARM: new cache maintenance api for iommu mem flush
> 
> non-coherent IOMMUs need to make sure that the
> data held in the caches need to be visible for the
> MMU hardware. A new L1 cache maintenance api has been
> created to handle this. Thanks to RMK's suggestions on
> creating a dedicated API for this purpose.
> 
> ref:
> http://marc.info/?l=linux-kernel&m=131316512713815&w=2
> 
> Signed-off-by: Ramesh Gupta G <grgupta@...com>
> ---
>  arch/arm/include/asm/cacheflush.h |   17 +++++++++++++++++
>  arch/arm/include/asm/glue-cache.h |    1 +
>  arch/arm/mm/proc-macros.S         |    1 +
>  3 files changed, 19 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/arm/include/asm/cacheflush.h
> b/arch/arm/include/asm/cacheflush.h
> index d5d8d5c..2b4f5aa 100644
> --- a/arch/arm/include/asm/cacheflush.h
> +++ b/arch/arm/include/asm/cacheflush.h
> @@ -84,6 +84,11 @@
>   *		- kaddr  - page address
>   *		- size   - region size
>   *
> + *     flush_mem(start, end)
> + *
> + *             Clean and invalidate the specified virtual address range.
> + *             - start  - virtual start address
> + *             - end    - virtual end address

You're missing a blank line here.

Also, "flush_mem" is a very lame name - it tells us nothing about what the
purpose of this new API is.  Should it be used for when the CPU MMU TLB
entries are changed?  What about if we're suspending, should it be used
then?  What about if we're performing DMA - should it be used for that
memory too?

Please, give it a better name which describes what it is for.

> diff --git a/arch/arm/mm/proc-macros.S b/arch/arm/mm/proc-macros.S
> index 2d8ff3a..f48a5ab 100644
> --- a/arch/arm/mm/proc-macros.S
> +++ b/arch/arm/mm/proc-macros.S
> @@ -307,6 +307,7 @@ ENTRY(\name\()_cache_fns)
>  	.long	\name\()_dma_map_area
>  	.long	\name\()_dma_unmap_area
>  	.long	\name\()_dma_flush_range
> +	.long	\name\()_flush_mem
>  	.size	\name\()_cache_fns, . - \name\()_cache_fns
>  .endm

This will immediately break the kernel compilation.  Therefore, your
patch is incomplete and unsuitable for applying.
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