On Mon, Aug 29, 2011 at 2:23 PM, Scott Wood <scottw...@freescale.com> wrote:
> On 08/29/2011 03:58 PM, Anton Staaf wrote:
>> On Mon, Aug 29, 2011 at 1:47 PM, Scott Wood <scottw...@freescale.com> wrote:
>>> 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.
>>
>> 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
>
>
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