Date: Thu, 24 Mar 2016 16:44:40 +0100 From: sylvain@sylvaingarrigues.com To: freebsd-arm <freebsd-arm@freebsd.org> Subject: Booting kernel.bin directly on Raspberry Pi / external DTB support Message-ID: <83488D96-F585-4A89-B53A-8E2E60BA3BD3@sylvaingarrigues.com>
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Hello, I have written a small (ugly) patch to be able to boot a kernel directly = without the ubldr loader while still using an external DTB (Linux-style = booting may pass the DTB location pointer in the r2 register). The patch is here: https://reviews.freebsd.org/differential/diff/14577/ = <https://reviews.freebsd.org/differential/diff/14577/>=20 I tested my patch successfully with the QEMU emulator with the -dtb = option available in recent versions, using a VERSATILEPB kernel without = FDT_STATIC. # qemu-system-arm -M versatilepb -m 128M -kernel versatile.flash -cpu = arm1176 -dtb versatilepb.dtb FYI, once the kernel is built, here is the script to build the = versatile.flash (adapted from gonzo, no longer need to clear the r0-r3 = registers): https://reviews.freebsd.org/P92 = <https://reviews.freebsd.org/P92>; I also tested successfully my patch on my Raspberry Pi 2 using U-BOOT = and the RPI2 kernel with my patch applied (and the LINUX_BOOT_ABI = option): u-boot> fatload mmc 0 0x200000 kernel.bin u-boot> go 0x200000 That works. So now I thought I could even bypass u-boot and launch kernel.bin = directly from the Pi firmware=E2=80=A6 But it doesn=E2=80=99t work, I = don=E2=80=99t understand why, and that is why I am writing here. Here is the config.txt which I thought would work: kernel=3Dkernel.bin (instead of u-boot.bin) kernel_address=3D0x200000 (line added because a FreeBSD kernel needs to = be loaded on a 1MB or 2MB boundary) device_tree=3Drpi2.dtb device_tree_address=3D0x100 disable_commandline_tags=3D1 What am I missing? Is it even possible to boot kernel.bin directly on = the Pi (with my patch)? I found this static minimalist loader from = Andrew here: = https://github.com/freebsd/freebsd/commit/074d37d46c3f9b282cd2d849d997b1b3= 9acd710c = <https://github.com/freebsd/freebsd/commit/074d37d46c3f9b282cd2d849d997b1b= 39acd710c> - does it mean such a loader is necessary before the kernel? Thanks, Sylvain PS: I know the =C2=AB official and supported =C2=BB way of booting = FreeBSD on the Pi is the u-boot + ubldr combination. I just would like = to finish this experiment and understand why kernel.bin cannot be booted = directly.=
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