On Sunday 05 February 2012 11:49 AM, Simon Glass wrote:
Hi,
On Sat, Feb 4, 2012 at 1:15 AM, Aneesh V<ane...@ti.com> wrote:
Hi Dirk,
On Friday 03 February 2012 12:55 PM, Dirk Behme wrote:
Hi,
on i.MX6 devices, e.g. ARM2 or SabreLite, the ROM boot loader copies the
U-Boot image from the boot device, e.g. the SD card, to the main memory.
This does mean that U-Boot is started in RAM.
With this, one might wonder why any relocation RAM -> RAM is done anyway
and if this could be skipped?
Looking into the details shows that board_init_f() in
arch/arm/lib/board.c and relocate_code() in arch/arm/cpu/armv7/start.S
[1] are involved in this.
In board_init_f() the relocation destination address 'addr' is
calculated. This is basically at the end of the available RAM (- some
space for various stuff like TLB tables etc.). At SabreLite this results
in 0x4FF8D000.
By the boot loader, the U-Boot is loaded to
CONFIG_SYS_TEXT_BASE 0x17800000
This results in relocate_code() copying U-Boot from RAM 0x17800000 to
RAM 0x4FF8D000.
Setting CONFIG_SYS_TEXT_BASE to the relocation destination address
0x4FF8D000 does avoid the (unnecessary?) copy by
cmp r0, r6
moveq r9, #0 /* no relocation. relocation offset(r9) = 0 */
beq clear_bss /* skip relocation */
in relocate_code().
But:
1) The resulting image still runs without the relocation
(CONFIG_SYS_TEXT_BASE 0x4FF8D000). But e.g. the U-Boot command line
doesn't work properly any more. Most probably this is because not only
the copy is skipped by the 'beq clear_bss', but the whole 'fix .rel.dyn
relocations' is skipped too.
2) It's hard to set CONFIG_SYS_TEXT_BASE at compile time to the
relocation address calculated at runtime in board_init_f() due to the
amount of #ifdef and runtime calculation done there. So finding a
generic approach which could easily defined in the config files to avoid
the relocation seems difficult.
I haven't really completely read your mail. But here is an
implementation I had provided long time back for ARM. But Wolfgang
didn't want to take it. You can see the patch and the following
discussion in this thread:
http://thread.gmane.org/gmane.comp.boot-loaders.u-boot/96352
From your patch Aneesh I evolved something that I still use - it deals
with the case where malloc cannot fit below the text area.
I find any sort of messing with the ICE startup a pain - although I
have often been able to script it. But for me I need to attach the
device tree to the binary and a few other things so I might as well
disable relocation at the same time. It also allows me to debug
seamlessly in board_init_f() as well as afterwards.
I will send a patch.
Great!
It would be good to get something in mainline despite the
protestations, if only to avoid all the work that people have to do to
figure out this problem.
I am always in favor of that:)
best regards,
Aneesh
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