[U-Boot] [PATCH] sandbox: Add improved RAM simulation

[Mike Frysinger]

On Tuesday 01 November 2011 14:37:24 Matthias Weisser wrote:
> I don't know the memory layout strategies for all the Linux/Unix variant
> out there. But typically text/bss/data is in the lower address range
> (some megs above 0) and in the upper range (right under kernel space)
> there is space used for stack and shared objects. Even with ASLR the
> address I used in the patch should be mappable.

relying on any address layout behavior is doomed to fail.  and in this case, 
it's unnecessary.  so let's not bother.

> >>> also, with Simon's other patch to md to use the remap func, the address
> >>> of our memory backing store doesn't matter.
> >> 
> >> Well, you are right. But with the posted patch you don't need any remap
> >> function and md/mm/mtest/mw works out of the box.
> > 
> > This is interesting. What is the test purpose of specifying a
> > particular virtual address for your memory?
> 
> Emulating the behavior of a u-boot on real hardware as close as
> possible. We have some chunk of memory at a given location. Thats it.
> With a minimum of additional work we can also simulate additional banks
> of RAM using multiple mmaps.

adding a CONFIG knob to control the virtual address of the memory is fine

> > If this is useful then we should make the mmap function fail if it
> > cannot honour the address, since otherwise presumably some tests will
> > fail.
> 
> Maybe. But on the other hand tests can always extract the actual address
> of RAM from gd->bd->bi_dram[0].start. If test use these address we can
> abandon the use of of fixed address. But I still thinks its nice to have
> an aligned address of RAM start as this is what we have on (all?) real
> hardware.

i'd rather see bi_dram die than extend it.  if you want to utilize the virtual 
memory, let's use the already existing map helper.
-mike
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