On Sep 21, 2012, at 6:54 AM, Robert Thorhuus wrote: >> -----Original Message----- >> From: Tabi Timur-B04825 [mailto:b04...@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 _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
