[U-Boot] [RFC] arm926ejs: fix jump to RAM nand_boot

[Sughosh Ganu]

hi Heiko,

On Tue Nov 02, 2010 at 09:55:46AM +0100, Heiko Schocher wrote:
> Hello Wolfgang,
> 
> Wolfgang Denk wrote:
> > Dear Heiko Schocher,
> > 
> > In message <4CCFAFE4.3000600 at denx.de> you wrote:
> >> - preloader copies first page of nand (nand_spl code) to
> >>   0xbb000000 (some cpu internal mem) and jumps to this address
> >> - nand_spl does lowlevelinit, relocate itself to TEXT_BASE (nand_spl code)
> > 
> > Why is this relocation needed? I understand that this 0xbb000000
> 
> Thats the question to solve ... don;t know, why nand_spl code
> on arm (and other architectures?) do this ... I try to have a look
> to find out, if we can run the nand_spl code complete from
> this address, and immedietaly copy u-boot from nand to ram ...

  I am not sure about all the ARM boards using nand_spl, but atleast
  on the hawkboard for which i have submitted patches, i have removed
  the call to relocate_code in nand_spl in V5. This is not needed at
  least on this board, as the nand_spl gets copied directly to the
  RAM.


> >> But as codesize changes (and with it relocation address) this
> >> is not a perfect solution.
> > 
> > Indeed. CONFIG_SYS_NAND_U_BOOT_SIZE should be dropped, and the avtual
> > value should be derived from the actual U-Boot image building
> > process.
> 
> Yep.


 But i have a doubt here. In case of hawkboard, the very reason we
 have a nand_spl booting stage is because the initial bootloader(RBL
 from TI) does not use the ECC layout as used by the davinci nand
 driver in u-boot. We flash the nand_spl separately by booting over
 UART[1]. In case, we compute the u-boot size dynamically, it would be
 needed to flash the nand_spl each time we build u-boot.

 Can we make a change such that we define an upper limit for the
 u-boot size, and the build produces a warning/error in case the
 u-boot size goes above this limit. We can avoid flashing the nand_spl
 each time using this method.

[1] - Please check doc/README.hawkboard
http://comments.gmane.org/gmane.comp.boot-loaders.u-boot/88139

-sughosh