[U-Boot] [PATCH] arm: Add option to disable code relocation

[Graeme Russ]

Hi Simon,

On Wed, Feb 8, 2012 at 6:12 PM, Simon Glass <sjg at chromium.org> wrote:

> Also make sure that the I-Cache is on as early as possible. Relocation
> is done with the d-cache off so is slow. Takes about 40ms for me from

Have a close look at the latest x86 patches (not yet pulled into mainline)
as an example of how this does not need to be the case. The sequence I
now use is:

  1) Initialise 'Cache-As-RAM' (CAR) - Cache cannot be used to cache
     SDRAM, otherwise the Stack and Global Data get trashed
  2) Create Stack and Global Data in CAR
  3) Initialise SDRAM
  4) Create a new stack in SDRAM
  5) 'Pivot' U-Boot - Move stack from CAR to SDRAM (U-Boot still running
     in Flash)
  6) Copy Global Data into SDRAM (adjust the global data pointer to point
     to the in-RAM copy)
  7) CAR is no longer used - Enable caching of SDRAM
  8) Copy U-Boot to RAM
  9) Perform relocation adjustments to in-RAM copy
 10) Jump to in-RAM copy
 11) Continue initialisation

> memory, but we do have things which can speed it up. But d-cache
> matters more than just about anything.

Now it may be the case (going by Wolfgang's comments) that some amount of
high-memory needs to be reserved, and the amount to be reserved is not
known until environment has been read. So there may be a need to put
the initial in-RAM stack and global data somewhere 'safe' while high-
memory space is calculated and U-Boot copied into RAM. Stack and global-
data can then be moved again (stack probably doesn't need moving, just
re-initialised at a new location) just below U-Boot. This would still be
a lot cheaper than copying U-Boot with D-Cache off

Regards,

Graeme