[PATCH 09/32] bcm2837-rpi-3-b.dts for 32bit arm
From: kraxel@redhat.com (Gerd Hoffmann)
Date: 2016-06-02 09:14:35
Also in:
linux-devicetree, lkml
Hi,
quoted
Well, it just includes the arm64 version as-is, so we don't have duplication. I'm open to suggestions to how handle this better. Symbolic link? Reference to ../../../arm64/boot/dts/broadcom/bcm2837-rpi-3-b.dts directly in the Makefile? I've seen arch/arm/boot/dts/Makefile uses globs on *.dts, so I suspect the later wouldn't be that straight forward.It's just weird that the arm64 file includes the .dtsi files from arch/arm/ and is then again included back from another file there. I can see two possible ways to handle this better: - leave the complete set of bcm2837 files in arch/arm and then have one reference from arch/arm64 per .dts that refers to just that file.
So basically do it the other way around. Would be a bit less messy indeed.
quoted hunk ↗ jump to hunk
- come up with a rule to also build the .dtb files in arch/arm64 when we run 'make dtbs' for arch/arm and leave this file there. The argument that one could use the same dtb with a 32-bit kernel should basically hold true for any arm64 system, it's not specific to rpi-3 really.
Yes, in theory. No, in practice. As far I know the rpi3 is the only 64bit soc where a almost identical 32bit version exists, so running 32bit kernels on a 64bit processor actually happens in practice and I expect this to continue. If you want create sdcard images which run on any rpi variant this is pretty much the only reasonable way to do it.
We don't normally test 32-bit kernels on 64-bit SoCs because 64-bit kernels are more efficient in a number of ways, and I'm sure there are bugs that prevent some systems from working (aside from how some machines cannot work because they don't have RAM below 4GB), but if this is now something that users are interested in, making it just work seems nicer than having a couple of board specific hacks.
See above, I have my doubts that the user interest in this expands to other boards. So I'd tend to pick the first option. cheers, Gerd