[U-Boot] [EXT] Re: Cavium/Marvell Octeon Support

[Aaron Williams <awilliams@marvell.com>]

On Thursday, October 31, 2019 3:36:10 AM PDT Wolfgang Denk wrote:
> Dear Aaron,
> 
> In message <1932577.QJWW3v3lL8@flash> you wrote:
> > We do this relocation as well, however the way we do it is by changing a
> > couple of TLB entries. This lets U-Boot begin execution from any memory
> > location, be it flash, L2 cache or RAM. It also lets us statically link
> > U-Boot to run at a fixed address, in our case 0xC0000000. The relocation
> > happens
> It seems you have missed the primary purpose of relocation.  The
> interesting thing is not the start address, but the end address of
> U-Boot in memory, as we alsways try to place the U-Boot code and data
> at the very end of the available memory (and yes, this includes
> systems which can cam with different memory sizes). Additionally, we
> want to be able to reserve additional memry at the end of RAM, above
> U-Boot, so it can even be kept across warm boots.  Features like
> protected RAM (PRAM), shared log buffers, shared video memory etc.
> come in to mind here.
This is exactly what we do. We use a high virtual address and always move it 
to the end of physical memory.

> 
> > This might be something to consider in the future on some platforms where
> > "relocation" could be performed by just adjusting the TLB or page tables.
> > MIPS makes this particularly easy.
> 
> This cannot be done, not without castrating U-Boot from a number of
> features that require allocation at the end of the available RAM,
> see above.
> 
> > That's fine. The code is actually quite small. It has some custom APIs
> > unique to our needs. We have need to call into the phy code from these
> > applications. I don't know if this could work with the general API or
> > not. One reason we did
> What exactly do you need this for?  Why don't you just link your
> code with the rest of U-Boot?
> 
We need it to obtain and modify the phy parameters. This is a custom 25G 
gearbox that needs a lot of hand holding. This may end up being a low priority 
(not the gearbox, but the API). It's only a few hundred lines of code (the 
API).

> 
> Best regards,
> 
> Wolfgang Denk

-Aaron