Dear Wolfgang,
On Tue, Jul 31, 2012 at 9:52 PM, Wolfgang Denk wd@denx.de wrote:
Can/should we use some existing mechanism? Or would it be considered a viable option to choose different beginning address for early heap, use it (in architecture-specific way) and keep the pointer to the beginning in GD. Then copy the early heap to memory before caches are flushed and in case of DM copy again data from early heap to new destinations that has been obtained through malloc() when it is initialized?
It is difficult (or actually impossible) to answer this, if you do not explain which concept you are talking about here, or why two copy operations would be needed, what "in case of DM" means (and which other cases exist), or how you intend to handle the problem of changing addresses (and thus pointers becoming incorrect) for each of such copy operations.
I have been given an advice by Graeme not to make early_malloc() as one-purpose thing for DM (i.e. not to implement DM tree relocation or special support for doing so in early_malloc routines).
Other guys working on DM wants AFAIK to create DM tree using early_malloc inside board_init_f(). The tree is going to have root and on some boards few extra elements, like 2 or 3 in this phase and each object has 16 bytes. Then they want to have this tree accessible (or at least a copy of the tree) in board_init_r(). They want to traverse the tree (by recomputing pointers) at some point in board_init_r(), allocate new tree objects using dlmalloc and copy the data into the new tree.
The concept I am thinking about is reserving space for early heap right after GD by same platform specific means (i.e. subtracting CONFIG_SYS_INIT_SP_ADDR). Then I would like to reserve space in RAM equal to used size of early_heap before relocation and memcpy the existing early_heap there (the same way GD are copied). Therefore we would have a copy of used early_heap in RAM and we can recompute pointers to traverse the tree in board_init_r().
Tomas