On 08/29/2011 03:12 PM, Anton Staaf wrote: > 1) Mikes's macro > > #define DMA_ALIGN_SIZE(size) \ > (((size) + CONFIG_SYS_CACHELINE_SIZE - 1) > > #define DMA_DECLARE_BUFFER(type, name, size) \ > void __##name[DMA_ALIGN_SIZE(size * sizeof(type))]; \ > type * name = __##name & ~(CONFIG_SYS_CACHELINE_SIZE - 1)); > > DMA_DECLARE_BUFFER(int, buffer, 100);
This doesn't compile, and it tries to round the buffer down below its starting point. After fixing the more obvious issues, I get "error: initializer element is not constant". There might be no way to express and-by-constant as a relocation. You could set the pointer at runtime, though, and remove some of the macrification: #define DMA_ALIGN_SIZE(size) \ ((size) + CONFIG_SYS_CACHELINE_SIZE - 1) #define DMA_ALIGN_ADDR(addr) \ (DMA_ALIGN_SIZE(addr) & (CONFIG_SYS_CACHELINE_SIZE - 1)) int buffer_unaligned[DMA_ALIGN_SIZE(100)]; int *buffer; some_init_func() { buffer = (int *)(DMA_ALIGN_ADDR((uintptr_t)buffer_unaligned)); } > 3) Use GCC specific alignment attribute: > > #define CACHLINE_ALIGNED __attribute__ ((aligned (CONFIG_SYS_CACHELINE_SIZE))) > > int buffer[100] CACHELINE_ALIGNED; > > Pros: The declaration of the buffer is even simpler and more obvious, > no use of alloca at all. > > Cons: This doesn't work in any version of GCC before October 2010. > Meaning that it probably doesn't work in whatever compiler you're > using. > > > It's really too bad that this isn't a usable solution. I suppose that > we could switch to it at some point when we expect U-Boot to only be > compiled by versions of GCC that support this. By the way, the > failure mode here is pretty bad. If you compile the above code with > an older GCC it will silently fail to align the variable. :( If the decision is made to depend on newer compilers, U-Boot could check for it and #error out if the compiler is too old (possibly just in the files that depend on this feature). -Scott _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot