-----Original Message----- From: Kumar Gala [mailto:galak@kernel.crashing.org] Sent: den 21 september 2012 14:50 To: Robert Thorhuus Cc: 'Tabi Timur-B04825'; u-boot@lists.denx.de Subject: Re: [U-Boot] arch/powerpc/lib/board.c:get_effective_memsize() for 4GB+ systems
On Sep 21, 2012, at 6:54 AM, Robert Thorhuus wrote:
-----Original Message----- From: Tabi Timur-B04825 [mailto:B04825@freescale.com] Sent: den 21 september 2012 13:37 To: Robert Thorhuus Cc: Kumar Gala; u-boot@lists.denx.de Subject: Re: [U-Boot] arch/powerpc/lib/board.c:get_effective_memsize() for 4GB+ systems
Robert Thorhuus wrote:
I really see the advantage of keeping this map you have. It is of course more compatible with different OSEs and you do not
need to do
anything special with 32/64 bit cores. But at the same time
you never
take advantage of a 64 bit core with this approach.
U-Boot is a boot loader, not an operating system. What is U-Boot supposed to do with more than 2GB of RAM?
How should I access my 24GB in U-Boot?
You should not!
So really you are saying that I should have a 2GB map
window in my
32-bit address space and then move this window depending on what memory I want to access? A bit cumbersome I must say. But ok.
Again, you're doing the wrong thing with U-Boot. It's a
boot loader.
It's supposed to find your OS, load it into memory, and
then boot it.
How about the U-Boot relocation?
As I see the code, it is not easy to decide where it should
relocate.
It will be either relocated to end of RAM or if we have
more than 4G
it will be at 4GB end.
It relocates to the end of RAM or the end of 2GB,
whichever is lower.
It ignores all memory above 2GB.
What if you want to place U-Boot at 16MB for instance? Or
if you do
not want a memory map hole at 4GB just because U-Boot
doesn't handle
more than that?
Again, you're missing the point about U-boot.
Last AND least I just want to say I'm used to creating
memory maps in
bootloader which holds for the OS. It seems the time has come to annihilate my illusion...
Yes, please kill it with fire!
-- Timur Tabi Linux kernel developer at Freescale
Hello Timur!
You really used the machine gun there ;)
Ok. I'll just answer your 2GB+ usage question:
Testing! No I will not be using much memory at all for
functionality. But the memory needs to be tested. What is your proposal for that then?
And I see U-Boot as the first software place for test and
debug. Maybe I want to read out RAM contents?
Robert,
We have seen some cases for u-boot to access >4G of memory directly. However, the effort to get u-boot to be a 64-bit clean just has never warranted the investment for the few minor cases people have raised for wanting to address >4G directly.
The one case I usually hear about is DDR test. We suggest its easier to try and getting DDR testing to utilize a window scheme into memory than it is for one to go make u-boot 64-bit.
:)
- k
Hello Kumar!
Ok. Since this seems to be the verified way I'll walk it. I'll change the DDR testing to be "small" window based.
Still I wonder why the choice was made to have U-Boot relocate in high memory rather than low memory and also not making it easy to configure the relocation.
BR Robert