Dear Aneesh V,
In message 4DD24BD6.5060608@ti.com you wrote:
Would it be possible to do this even _before_ relocation, so to speed up memory accesses during relocation? Of course, proper invalidates/ flushes will be needed before jumping to the RAM address, but I guess this would save a bit of boot times?
I intentionally kept it after relocation to avoid un-necessary complexities.
Yes, I can understand this. Do you plean to extend this to include relocation n a later step?
Relocation is a case of self-modifying code. In Harvard architectures like armv7 there will be coherency issues unless we flush the entire D-cache(range based operation may be equally or more expensive) and invalidate the entire I-cache.
I would not call this self-modifying code.
Regarding the need to flush/invalidate caches when jumping to RAM: yes, we have to flush the D-cache to make sure all data actually has hit the memory. But there should be no need to invalidate the I-cache as we have never been fetching any instructions from this address range, so there cannot be any incorrect entries in cache.
Or am I missing something?
So, in effect everything has to be flushed to memory before you jump to the new location. There may be a small advantage because flushing from cache allows for bursting to the DDR where as bursting is not possible when d-cache is disabled. But I think this is not worth the trouble.
Well, all the data copy will also use cached writes, which are much faster. I think this will result in measurable time differences.
Best regards,
Wolfgang Denk