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

[Simon Glass]

Hi Graeme,

On Wed, Feb 8, 2012 at 7:38 PM, Graeme Russ <graeme.russ at gmail.com> wrote:
> 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.

Yes I went through these carefully at the time - remember the
discussion about board_init_f_r()? I hope we can do something similar
on generic board, but of course in general there is a trade-off
between the time to set up the MMU tables and the time to do the copy.

>
> 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

Yes. With a chance of 'epsilon' of this patch getting in, I am
dropping it. While I agree what you have done is much better than what
was there, I have my eyes on the higher goal of unifying the board
init code for all archs.

Will revisit when/if generic board goes into mainline. If you have
time, please take a look at that series.

Regards,
Simon

>
> Regards,
>
> Graeme