On Mon, Aug 29, 2011 at 2:23 PM, Scott Wood scottwood@freescale.com wrote:
On 08/29/2011 03:58 PM, Anton Staaf wrote:
On Mon, Aug 29, 2011 at 1:47 PM, Scott Wood scottwood@freescale.com wrote:
On 08/29/2011 03:12 PM, Anton Staaf wrote:
- 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.
You are correct. I wrote that one as a modification of mikes initial proposal. I should have caught the incorrect rounding when I did. The patch that Lukasz sent titled "dcache: Dcache line size aligned stack buffer allocation" has a correct implementation.
With the version in that patch I get the slightly different "error: initializer element is not computable at load time". Seems like whether you cast the address to (type *) or (void *) determines which error you get. This is with GCC 4.5.1 (powerpc) and 4.6.0 (x86). Maybe it's arch-dependent, based on available relocation types.
Also, shouldn't the array be of type "char" rather than "char *"?
Yes, you are correct, it should be a char. That may be the problem.
How do you make the declaration static?
you can't with this version of the macro. Are there cases where you need the buffer to be static?
Thanks, Anton
After fixing the more obvious issues, I get "error: initializer element is not constant".
I think this requires the use of -std=c99 or GCC extensions. More specifics can be found here: http://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html
-std=c99 doesn't help.
The problem isn't the array itself, it's the pointer initializer.
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)); }
:) This was one of my suggestions earlier on a different thread. It was rejected there, I believe because it makes things less clear.
So, the complex macro is bad because it obscures things, and this version is bad because it doesn't? :-)
-Scott