Date: Fri, 25 Mar 2016 18:55:11 +0100 From: Sylvain Garrigues <sylgar@gmail.com> To: Warner Losh <imp@bsdimp.com> Cc: ticso@cicely.de, freebsd-arm <freebsd-arm@freebsd.org> Subject: Re: Booting kernel.bin directly on Raspberry Pi / external DTB support Message-ID: <97BB142C-D335-469B-9514-D1210E869C5D@gmail.com> In-Reply-To: <CANCZdfrhm5NSCXehkDc%2BDa4cxYhbU_NnEopR__e_a0CgajEL3A@mail.gmail.com> References: <1CCA59DC-5539-4CFB-81BA-0112E2120B3B@gmail.com> <20160325052509.GE48704@cicely7.cicely.de> <CANCZdfrhm5NSCXehkDc%2BDa4cxYhbU_NnEopR__e_a0CgajEL3A@mail.gmail.com>
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Thank you.=20 I wanted to boot the kernel directly so as to: 1/ remove the dependency on a 3rd party loader 2/ reduce boot time and make it comparable with NetBSD and Linux (which = don=E2=80=99t use u-boot) NetBSD and Linux on the Pi boot so much faster than our FreeBSD image: = less than 1 second after power-up, the first kernel copyright line = appears on my LCD. For the FreeBSD images, the longest part is ubldr = loading the kernel. It takes around 4/5 seconds (with the same SD card). I used recent u-boot versions (the current u-boot-rpi2 port is getting = old and is not in sync with the u-boot-rpi port recently updated), tried = with dcache enabled, but the boot process still takes several seconds, = most of the time being spent in ubldr loading the kernel. I have no idea how we could improve the booting time? I wanted to = experiment with booting the kernel directly as the first ARM program on = my Pi, but as you explained I need some init code. I managed to compile = Andrew=E2=80=99s one = (https://github.com/freebsd/freebsd/commit/074d37d46c3f9b282cd2d849d997b1b= 39acd710c = <https://github.com/freebsd/freebsd/commit/074d37d46c3f9b282cd2d849d997b1b= 39acd710c>) but I don=E2=80=99t know how to use it. Andrew, if you read = this ;-) Best, Sylvain. =20 > Le 25 mars 2016 =C3=A0 06:48, Warner Losh <imp@bsdimp.com> a =C3=A9crit = : >=20 >=20 >=20 > On Thu, Mar 24, 2016 at 11:25 PM, Bernd Walter = <ticso@cicely7.cicely.de <mailto:ticso@cicely7.cicely.de>> wrote: > On Thu, Mar 24, 2016 at 04:29:26PM +0100, Sylvain Garrigues wrote: > > 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/>; > > > > 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>; <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??? But it doesn???t work, I don???t = 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><https://github.com/freebsd/freebsd/commit/074d37d46c3f9b282cd2d= 849d997b1b39acd710c = <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. >=20 > I don't know if it is part of ubldr, or if there is any additional = code, > which runs before ubldr, but the Pis won't boot with the ARM CPU. > Somewhere in the boot path is GPU bootcode, which then enables the ARM > CPU. > You also need low level HW init, such as setting up the clocks and = RAM, > which is not done in the Kernel. >=20 > What you are missing it the hardware init code that's in u-boot.bin. = This code sets up > the board after the on-board GPU loads it into the ARM's address = space. That code > sets up the ARM side of the world and hands off the code to ubldr = which finds the dtb > and does the normal /boot/loader things as well (loading modules, = setting tunables > and the like) then hands off to the kernel. You can eliminate ubldr = without a huge > amount of effort, as you've found. However, eliminating u-boot.bin is = going to be > a lot more work/ >=20 > tl;dr: The interface between u-boot.bin and ubldr/kernel.bin is quite = a bit different > than between the initial bootstrap and u-boot.bin. So you can't just = drop in kernel.bin > and have it work without replicating that interface. >=20 > Warner
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