[U-Boot] [PATCH 1/2] common.h: Introduce DEFINE_CACHE_ALIGN_BUFFER

[Mike Frysinger]

On Friday 20 July 2012 17:50:33 Tom Rini wrote:
> On 07/20/2012 02:47 PM, Mike Frysinger wrote:
> > On Friday 20 July 2012 07:31:47 Marek Vasut wrote:
> >> Dear Mike Frysinger,
> >> 
> >>> On Saturday 07 July 2012 23:08:14 Marek Vasut wrote:
> >>>> +/* DEFINE_CACHE_ALIGN_BUFFER() is similar to
> >>>> ALLOC_CACHE_ALIGN_BUFFER, but it's purpose is to allow
> >>>> allocating aligned buffers outside of function scope.  Usage
> >>>> of this macro shall be avoided or used with extreme care! */
> >>>> +#define DEFINE_CACHE_ALIGN_BUFFER(type, name, size) +	static
> >>>> char __##name[roundup(size * sizeof(type),
> >>>> ARCH_DMA_MINALIGN)] +			__aligned(ARCH_DMA_MINALIGN); +
> >>>> static type *name = (type *)__##name;
> >>> 
> >>> how is this any different from doing: static __u8 foo[1234]
> >>> __aligned(ARCH_DMA_MINALIGN);
> >> 
> >> Does __aligned() align both start of the buffer downwards and end
> >> of it upwards ?
> > 
> > it guarantees the start is aligned.  i don't believe it does any
> > tail padding.
> > 
> > that said, you've added just 1 consumer, but it uses in function
> > scope, so i don't see why you had to define a new helper in the
> > first place.  the existing one would work fine shouldn't it ?
> 
> The rough outline of the problems are:
> - We need to have buffers that are multiple of cache size, for clearing.
> - Today we know ehci-hcd had a problem.  We also know other drivers /
> layers have problems, but they aren't as readily breakable.
> 
> That's why we put the macro in <common.h> rather than a USB header.

that wasn't the question.  no one in the tree needs the new macro at all, 
regardless of what header it lives in.  i guess the answer is that some code 
in the future (which hasn't been merged) might use it.
-mike
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