Folks,
We're going to be seeing more platforms with larger physical addresses (PA) than virtual addresses (VA) supported in u-boot, and this kind of ruins the current assumption inherent in much of u-boot that VA == PA. On ppc, we've begin implementing the ability to actually translate VAs to PAs and vice-versa. But this brings up the question of, when I type an address on the command line, what exactly am I specifying? Is that a virtual address, or a physical address?
Wolfgang and I talked about this on IRC a bit earlier, and what we're proposing is this:
- The addresses taken as arguments to and printed out by current commands will be interpreted as virtual addresses. This will minimize the changes required to uboot to get this working, and allows command code to dereference the address given directly as a pointer - poking around the code, I believe this to be the more common case. This could really go either way - we could specify the physical address here, but I think that is more counter to the assumptions of the existing code. Having a VA is slightly awkward in some of the code - the flash code comes to mind, but the particular flash code I've looked at is so confused with VA vs PA that I don't think it really matters which way we go.
- Initially, a xlat (or insert better name here) command-line command will be added to give you a PA given a VA, and vice-versa.
- Going forward, commands will be extended to take either a VA or PA at the command line, with the syntax for this TBD and per argument (i.e. if a command takes multiple addresses, each one can be either a va or pa, and they can be intermingled). The default will remain VA if no modifier is specified.
Note that unless your platform actually has enabled configs with VA != PA (which is just MPC8641D at the moment, as far as I know), things will look exactly the same as they always have.
Comments? I'm looking for some consensus here before I spend my weekend writing a whole bunch of code.
Cheers, Becky