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

[Tom Rini]

On Sat, Jul 21, 2012 at 01:22:40PM -0400, Mike Frysinger wrote:
> 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.

Er, between drivers/usb/host/ehci-hcd.c and drivers/usb/eth/smsc95xx.c
the three new macros are used today.

-- 
Tom