Re: [PATCH 5/8] ARM: dma-mapping: move all dma bounce code to separate dma ops structure

[Arnd Bergmann <arnd@arndb.de>]

On Monday 20 June 2011, Marek Szyprowski wrote:
> On Monday, June 20, 2011 4:43 PM Russell King - ARM Linux wrote:
> 
> > On Mon, Jun 20, 2011 at 09:50:10AM +0200, Marek Szyprowski wrote:
> > > This patch removes dma bounce hooks from the common dma mapping
> > > implementation on ARM architecture and creates a separate set of
> > > dma_map_ops for dma bounce devices.
> > 
> > Why all this additional indirection for no gain?
> 
> I've did it to really separate dmabounce code and let it be completely 
> independent of particular internal functions of the main generic dma-mapping
> code.
> 
> dmabounce is just one of possible dma-mapping implementation and it is really
> convenient to have it closed into common interface (dma_map_ops) rather than
> having it spread around and hardcoded behind some #ifdefs in generic ARM
> dma-mapping.
> 
> There will be also other dma-mapping implementations in the future - I 
> thinking mainly of some iommu capable versions. 
> 
> In terms of speed I really doubt that these changes have any impact on the
> system performance, but they significantly improves the code readability 
> (see next patch with cleanup of dma-mapping.c).

Yes. I believe the main effect of splitting out dmabounce into its own
set of operations is improved readability for people that are not
familiar with the existing code (which excludes Russell ;-) ), by
separating the two codepaths and losing various #ifdef.

The simplification becomes more obvious when you look at patch 6, which
removes a lot of the code that becomes redundant after this one.

Still, patches 5 and 6 are certainly not essential, nothing depends on
that and if Russell still doesn't like them, they can easily be dropped.

	Arnd

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