Messages in this thread | | | Subject | Re: [PATCH 1/2] DMA buffer alignment annotations | From | Benjamin Herrenschmidt <> | Date | Sat, 22 Dec 2007 08:25:41 +1100 |
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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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