Date: Thu, 24 Dec 2015 16:40:13 +0100 From: Sylvain Garrigues <sylgar@gmail.com> To: Ian Lepore <ian@freebsd.org> Cc: Tim Kientzle <tim@kientzle.com>, freebsd-arm <freebsd-arm@freebsd.org> Subject: Re: Booting the ELF kernel without ubldr on Raspberry Pi Message-ID: <BD124AF0-68E2-457A-9B63-6BE312F218E5@gmail.com> In-Reply-To: <1450970414.25138.238.camel@freebsd.org> References: <C6819C94-DF61-447F-AC61-FD3E061A6F76@gmail.com> <32849B9F-C7B8-4A86-B8F1-043F62D2E64C@kientzle.com> <8F62699C-126D-492D-8B7E-8C250ED5BC07@gmail.com> <1450970414.25138.238.camel@freebsd.org>
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Hello Ian,
I=E2=80=99m using u-boot from the ports (sysutils/u-boot-rpi2). It =
doesn=E2=80=99t display anything about cache being enabled.
I was just comparing the time it takes to have the Linux kernel prints =
its first lines, and the time it takes for the FreeBSD kernel to print =
its own (the =C2=AB Copyright =C2=BB line) when used with u-boot+loader.
For the former, it=E2=80=99s under a second, for the latter it=E2=80=99s =
about 3-4 seconds (mainly spent when the loader loads the elf kernel).
So I was wondered how they made it and was led to believe the Linux =
kernel is compressed (and self-extracting), leading to less loading time =
from the SD card which apparently is the bottleneck.
So since the FreeBSD kernel has no =C2=AB self-extracting =C2=BB =
feature, and since ubldr doesn=E2=80=99t seem to support the extracting =
of a gzip kernel (well it seems to work with LOADER_GZIP_SUPPORT but I =
see no gain), I was trying to use the compression and extraction feature =
of u-boot with the use of recent mkimage with support for lzma =
compression. I thought I could boot directly a LZMA compressed =
kernel.bin with mkimage, without ubldr. But I forgot about the kernel =
expecting a variable with the DTB address, which is set up by ubldr, so =
I give up and will wait to see if someone is interested in implementing =
a self-extracting kernel in the future.
Best,
Sylvain =20
> Le 24 d=C3=A9c. 2015 =C3=A0 16:20, Ian Lepore <ian@freebsd.org> a =
=C3=A9crit :
>=20
> On Thu, 2015-12-24 at 11:51 +0100, Sylvain Garrigues wrote:
>> If I look at what gonzo did for VERSATILEPB, I think it can be done
>> easily by writing a tiny assembly code that does something like what
>> he did:
>>=20
>> # set r0..r3 to zero
>> /usr/bin/printf "\0\0\240\343" > ${WORKDIR}/first_commands
>> /usr/bin/printf "\0\020\240\343" >> ${WORKDIR}/first_commands
>> /usr/bin/printf "\0\040\240\343" >> ${WORKDIR}/first_commands
>> /usr/bin/printf "\0\060\240\343" >> ${WORKDIR}/first_commands
>>=20
>> # jump to kernel entry point
>> /usr/bin/printf "\001\366\240\343" >> ${WORKDIR}/first_commands
>>=20
>> # install kernel
>> [ ! -d ${WORKDIR}/_.kernel.bin ] && mkdir ${WORKDIR}/_.kernel.bin
>> board_default_installkernel ${WORKDIR}/_.kernel.bin
>>=20
>> dd of=3D$VERSATILEPB_FLASH bs=3D1M count=3D4 if=3D/dev/zero
>> dd of=3D$VERSATILEPB_FLASH bs=3D1 conv=3Dnotrunc
>> if=3D${WORKDIR}/first_commands
>> dd of=3D$VERSATILEPB_FLASH bs=3D64k oseek=3D15 conv=3Dnotrunc
>> if=3D${WORKDIR}/_.kernel.bin/boot/kernel/kernel.bin
>>=20
>> The only problem for the Raspberry pi is that, if I am correct, the
>> DTB is modified by the firmware (bootcode.bin) so I can=C2=B4t =
statically
>> compile the DTB in the kernel like for VERSATILEPB :( I would need to
>> mimic what loader does and create a kernel environment variable which
>> contains the address to the DTB.
>>=20
>> This is a good exercice, but it doesn=C2=B4t solve my project which =
is to:
>>=20
>> 1/ have a self-extracting kernel or have a loader which uncompress
>> the kernel, so that it takes much less time to start (my benchmark is
>> raspbian or openelec).=20
>> =3D=3D> I compiled ubldr with LOADER_GZIP_SUPPORT and compressed =
kernel
>> to kernel.gz, reducing the size by 2. The loader does manage to load,
>> uncompress and boot the kernel.gz, but the loading time is worse than
>> when uncompressed, so I=C2=B4m stuck I don=C2=B4t know what=C2=B4s =
wrong?
>>=20
>> 2/ have the bootloader / kernel display a nice splash screen while
>> the kernel boots
>> =3D=3D> for that I looked at u-boot splash screen but the quality of =
the
>> rendering is too poor (8-bit bitmap). I looked at the VT frame buffer
>> but the slash screen feature is also limited. So I might now look
>> into the misc/raspberrypi-userland port and understand how the
>> hello_jpeg sample code does that with the GPU, then I plan to port it
>> in the kernel initialization code, not sure it=C2=B4s going to work)=20=
>=20
> What version of u-boot are you using for this? I don't understand the
> obsession with the time it takes to load the kernel unless something
> unusual is happening. On my systems the time it takes to load a
> kernel, whether it's u-boot or ubldr doing the work, is pretty much
> exactly the time it takes to read the media the kernel is on. On an
> sdcard that's usually a few seconds, on gigabit ethernet it tends to =
be
> far less than one second. But all of that assumes that caching is
> enabled in u-boot, and it wasn't in some of the older ports.
>=20
> When u-boot starts does it say anything about the caches being enabled
> or disabled? Is the dcache command available? If not, it's probably
> not enabled, and a newer u-boot may fix the problem. I hope to be
> updating all our u-boot ports over the next month or so.
>=20
> -- Ian
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