Hi Tim, On Tue, 18 Jul 2023 at 09:59, Tim van der Staaij | Zign <tim.vandersta...@zigngroup.com> wrote: > > Hello, > > When I was using U-Boot with a dart_6ul board I occasionally had fitimages > that U-Boot would attempt to boot just fine, but the kernel wouldn't actually > boot. Debugging found that this was correlated with the header length of the > fitImage. Then I noticed this remark in doc/usage/environment.rst about > fdt_high: > > >If this is set to the special value 0xffffffff (32-bit machines) or > >0xffffffffffffffff (64-bit machines) then the fdt will not be copied at > >all on boot. For this to work it must reside in writable memory, have > >sufficient padding on the end of it for u-boot to add the information > >it needs into it, and the memory must be accessible by the kernel. > >This usage is strongly discouraged however as it also stops U-Boot > >from ensuring the device tree starting address is properly aligned > >and a misaligned tree will cause OS failures. > > And indeed, fdt_high is set to 0xffffffff in the include/configs/dart_6ul.h > that I was using. Since mkimage only guarantees 32-bit alignment of the > device tree blob within the fitimage, and not the 64-bit alignment that Linux > requires, this is basically a 50/50 coin flip. Something simple like adding a > few characters to the description string in the fitimage header can make or > break the alignment. > > Personally I fixed this by removing the fdt_high altogether, which makes > U-Boot copy the device tree to an appropriate location. I assume this only > works in my situation because I only have half a GiB of RAM and therefore do > not have any high memory. I can imagine my fix would be problematic for board > variants with more RAM, the setting doesn't exist without a reason of course. > > It looks like this issue is not limited to my board; the same usage of > fdt_high can be found in many other board configs. I'm not going to suggest > what the best fix is because I lack detailed knowledge, but I will pitch that > perhaps omitting fdt_high by default is at least preferable to a value that > is "strongly discouraged" and causes Linux boot failures somewhat arbitrarily.
I wonder if we should adjust mkimage to use -B 8 as the default? Regards, Simon
