[U-Boot] arch/powerpc/lib/board.c:get_effective_memsize() for 4GB+ systems
robert.thorhuus at ericsson.com
Fri Sep 21 13:54:38 CEST 2012
> -----Original Message-----
> From: Tabi Timur-B04825 [mailto:B04825 at freescale.com]
> Sent: den 21 september 2012 13:37
> To: Robert Thorhuus
> Cc: Kumar Gala; u-boot at 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
> > 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
You really used the machine gun there ;)
Ok. I'll just answer your 2GB+ usage question:
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?
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