On Fri, 2007-12-21 at 09:39 +0000, Russell King wrote:
> > +#ifndef ARCH_MIN_DMA_ALIGNMENT
> > +#define __dma_aligned
> > +#define __dma_buffer
> > +#else
> > +#define __dma_aligned __attribute__((aligned(ARCH_MIN_DMA_ALIGNMENT)))
> > +#define __dma_buffer __dma_buffer_line(__LINE__)
> > +#define __dma_buffer_line(line) __dma_aligned;\
> > + char __dma_pad_##line[0] __dma_aligned
>
> You introduce __dma_buffer_line() if ARCH_MIN_DMA_ALIGNMENT is set but
> not if it isn't...
Yup, it's not meant to be used outside of __dma_buffer...
.../...
> > +then dev->buffer will be safe for DMA on all architectures. On a
> > +cache-coherent architecture the members of dev will be aligned exactly
> > +as they would have been without __dma_buffer; on a non-cache-coherent
> > +architecture buffer and field2 will be aligned so that buffer does not
> > +share a cache line with any other data.
> > +
>
> ... but it's not described. What's the purpose of it, and why would it
> only be used on CPUs with ARCH_MIN_DMA_ALIGNMENT set?
Hrm, I'm not the best at writing exlanations, care to send a patch ? :-)
Cheers,
Ben
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