Hi,

Debian provides a kernel for Raspberry Pi Zero (W) and 1, but that targets
the armel architecture. I want to compile a/the Debian kernel that does use the HW capabilities of the RPi 0/1, similarly to how raspbian.org recompiles
the Debian packages. Except AFAIK the Debian kernel.

I know that Debian won't change their RPi kernel for armel, but this is for private use. But I don't know what the best way to go about that is.

I found the following link wrt building a cross compiler https://solarianprogrammer.com/2018/05/06/building-gcc-cross-compiler-raspberry-pi/
which in turn references https://preshing.com/20141119/how-to-build-a-gcc-cross-compiler/
and that does look promising.

But before diving full into it, I'd like to know whether this is the proper approach or not. And if someone has good/better links, I'd appreciate it if you'd share them :-)

While I (technically) could setup a system to compile natively, I want to use cross compilation (on amd64 PC). I think it would otherwise take days.
But knowing how to compile natively would be nice too.
I do know how to compile Debian's kernels, both natively and cross building.

Cheers,
Diederik
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On 10/23/22 16:31, Diederik de Haas wrote:

Hi,

Debian provides a kernel for Raspberry Pi Zero (W) and 1, but that targets the armel architecture. I want to compile a/the Debian kernel that does use the
HW capabilities of the RPi 0/1, similarly to how raspbian.org recompiles
the Debian packages. Except AFAIK the Debian kernel.

I know that Debian won't change their RPi kernel for armel, but this is for private use. But I don't know what the best way to go about that is.

I found the following link wrt building a cross compiler https://solarianprogrammer.com/2018/05/06/building-gcc-cross-compiler-raspberry-pi/
which in turn references https://preshing.com/20141119/how-to-build-a-gcc-cross-compiler/
and that does look promising.

But before diving full into it, I'd like to know whether this is the proper approach or not. And if someone has good/better links, I'd appreciate it if you'd share them :-)

While I (technically) could setup a system to compile natively, I want to use cross compilation (on amd64 PC). I think it would otherwise take days.

Probably an over estimate unless you don't have any SSD hardware for
workspace.
 I do, 240Gigs on a startech usb to sata adaptor  and I have built an
armhf version
of 4.19 in under an hour on an rpi4. Working on a u-sd card,
you'll be abusing the card and quite a few hours. I would not even try
it on less than a 64G u-sd.
You'll surely kill an 8G u-sd card by writing it to death..

But knowing how to compile natively would be nice too.
I do know how to compile Debian's kernels, both natively and cross building.

Cheers,
Diederik

Cheers, Gene Heskett.
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/>

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Diederik de Haas <didi.debian@cknow.org> writes:

Hi,

Debian provides a kernel for Raspberry Pi Zero (W) and 1, but that targets the armel architecture. I want to compile a/the Debian kernel that does use the
HW capabilities of the RPi 0/1, similarly to how raspbian.org recompiles
the Debian packages. Except AFAIK the Debian kernel.

I know that Debian won't change their RPi kernel for armel, but this is for private use. But I don't know what the best way to go about that is.

I found the following link wrt building a cross compiler https://solarianprogrammer.com/2018/05/06/building-gcc-cross-compiler-raspberry-pi/
which in turn references https://preshing.com/20141119/how-to-build-a-gcc-cross-compiler/
and that does look promising.

I am probably missing some context but I wanted to point to the armel
cross compiler in Debian - gcc-arm-linux-gnueabi. Is there some reason
to build the cross-compiler yourself?

[...]

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Copy: debian-arm@lists.debian.org

On maandag 24 oktober 2022 11:16:42 CEST Punit Agrawal wrote:

I am probably missing some context but I wanted to point to the armel
cross compiler in Debian - gcc-arm-linux-gnueabi. Is there some reason
to build the cross-compiler yourself?

I don't want to build for armel, but for raspbian.org's variant of armhf,
which is not the same as Debian's armhf.
The RPi 0/1 fall somewhere in the middle of Debian's armel and armhf and
that's the whole reason raspbian.org was created.

But it can be that I'm looking at this problem all wrong and/or have some tunnel vision towards building a cross compiler.
That is an important reason for making this ML thread.

Cheers,
Diederik
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--- SoupGate-Win32 v1.05
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Diederik de Haas <didi.debian@cknow.org> writes:

On maandag 24 oktober 2022 11:16:42 CEST Punit Agrawal wrote:

I am probably missing some context but I wanted to point to the armel
cross compiler in Debian - gcc-arm-linux-gnueabi. Is there some reason
to build the cross-compiler yourself?

I don't want to build for armel, but for raspbian.org's variant of armhf, which is not the same as Debian's armhf.
The RPi 0/1 fall somewhere in the middle of Debian's armel and armhf and that's the whole reason raspbian.org was created.

Thanks for the context.

But it can be that I'm looking at this problem all wrong and/or have some tunnel vision towards building a cross compiler.
That is an important reason for making this ML thread.

IIUC, for the kernel, either compiler should be fine. The
documentation[0] for compiling the RPi Zero kernel seems to bear this
out - it even uses the "CROSS_COMPILE=arm-linux-gnueabihf-". If you've
got access to the hardware it should be easy to test before kicking off
the Debian kernel package build.

Hope that helps.

Regards,
Punit

[0] https://www.raspberrypi.com/documentation/computers/linux_kernel.html#cross-compiling-the-kernel

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On Tue, Oct 25, 2022 at 09:12:06AM +0200, Marcin Juszkiewicz wrote:

W dniu 25.10.2022 o 00:03, Punit Agrawal pisze:

IIUC, for the kernel, either compiler should be fine. The
documentation[0] for compiling the RPi Zero kernel seems to bear this
out - it even uses the "CROSS_COMPILE=arm-linux-gnueabihf-". If you've
got access to the hardware it should be easy to test before kicking off
the Debian kernel package build.

Raspbian uses own definition of armhf (armv6) while Debian (and other distros) use armv7 for armhf.

So using any documentation which mentions armhf and r/pi needs to be done in careful way.

The (early) Raspberry Pi 0/1 (and the Pi Zero v1 at least) are armv6 with hardware floating point when all the Linux distributions had already
decided on v7 and hardware floating point as armhf architecture.
Debian armel runs fine without recompilation at a slight penalty.

Raspbian history is effectively a port by interested Debian folk -
Raspberry Pi OS is subtly different (and includes non-free software
as part of the standard build).

Later models of Raspberry Pi run as v7 and hardware floating point so
Debian armhf runs natively.

Raspberry Pi OS is slowly moving to 64 bit but the earliest Pis are 32 bit only. Debian arm64 will run natively on Raspberry Pi 64 bit - the latest firmware vote will also mean that we can include Raspberry Pi firmware
in the installer for next version Bookworm.

Hope this helps,

Andy Cater

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W dniu 25.10.2022 o 00:03, Punit Agrawal pisze:

IIUC, for the kernel, either compiler should be fine. The
documentation[0] for compiling the RPi Zero kernel seems to bear this
out - it even uses the "CROSS_COMPILE=arm-linux-gnueabihf-". If you've
got access to the hardware it should be easy to test before kicking off
the Debian kernel package build.

Raspbian uses own definition of armhf (armv6) while Debian (and other
distros) use armv7 for armhf.

So using any documentation which mentions armhf and r/pi needs to be
done in careful way.

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On Tue, Oct 25, 2022, at 00:03, Punit Agrawal wrote:

Diederik de Haas <didi.debian@cknow.org> writes:

But it can be that I'm looking at this problem all wrong and/or have some
tunnel vision towards building a cross compiler.
That is an important reason for making this ML thread.

IIUC, for the kernel, either compiler should be fine. The
documentation[0] for compiling the RPi Zero kernel seems to bear this
out - it even uses the "CROSS_COMPILE=arm-linux-gnueabihf-". If you've
got access to the hardware it should be easy to test before kicking off
the Debian kernel package build.

That is correct: it's the same compiler backend, the only difference
between an arm-linux-gnuabihf- and an arm-linux-gnueabi- toolchain are
which CPU and floating pointing ABI are set when building with the
default flags. The kernel itself is always built as soft-float even
for armv7 using an armhf toolchain, and the CPU is always set to
the minimum configured target machine, so both compilers will produce
the same kernel binary.

Note that at the moment, you can build a kernel that works on
both armv6 and armv7 CPUs, or armv7 and armv8, but not armv5
and armv6/v7, or armv6 and armv8, and this limits what machines
can be enabled in a single kernel. I have a prototype kernel
patch that intends to change the way we build armv6 kernels,
so one can actually enable armv6 non-SMP support (Raspberry
Pi 0/1, OMAP2, i.MX3, s3c64xx, ...) in the default armel
kernel along with the ARMv5 targets (orion, kirkwood, pxa,
at91, omap1, imx2, suniv, ...), but no longer with ARMv7.

Arnd

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On Tue, Oct 25, 2022, at 11:15, Diederik de Haas wrote:

On Tuesday, 25 October 2022 10:02:09 CEST Andrew M.A. Cater wrote:

Debian armel runs fine without recompilation at a slight penalty.

It is exactly this 'slight penalty' that I want to verify.

I have a Zero W running Debian's armel kernel and I find that device to be annoyingly slow.
I also have a RPi 1 running raspbian.org's 4.9 kernel, which is a special kernel build by plugwash and compiled like the rest of raspbian.org packages, which I do not find (annoyingly) slow.

The difference between the two kernels is almost certainly unrelated
to the toolchain they are built with, and entirely based on the
kernel patches that are added on top of mainline as well as the
configuration.

If there is a huge difference, my first guess would be the CPU frequency scaling driver: if the CPU runs a different operating point, that
would have a much larger impact than anything the kernel itself
can do. Another obvious difference may be the GPU support: if you
the HDMI output, having an accelerated driver for it will feel
much faster than running on a plain framebuffer.

If you have a fast Raspbian kernel and a slow Debian kernel for
the same source version, can you take a look at the /boot/config-*
files, and the list of loaded kernel modules, to see if there
are any obvious differences?

Arnd

--- SoupGate-Win32 v1.05
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On Tuesday, 25 October 2022 10:02:09 CEST Andrew M.A. Cater wrote:

Debian armel runs fine without recompilation at a slight penalty.

It is exactly this 'slight penalty' that I want to verify.

I have a Zero W running Debian's armel kernel and I find that device to be annoyingly slow.
I also have a RPi 1 running raspbian.org's 4.9 kernel, which is a special kernel build by plugwash and compiled like the rest of raspbian.org packages, which I do not find (annoyingly) slow.
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This is a multi-part message in MIME format.

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On Tuesday, 25 October 2022 14:34:12 CEST Diederik de Haas wrote:

and entirely based on the kernel patches that are added on top of mainline as well as the configuration.

The patch set may be more substantial then I initially thought.
In 2015 I asked plugwash the general procedure to make a raspbian.org style kernel and my notes of that are attached.

Through that, I found that an 'update-rpi-patches' script was used (attached) and that adds https://github.com/raspberrypi/linux.git as remote.

I don't think I ever succeeded in building such a kernel though, probably also because I had ~0 experience with building a kernel at all. --nextPart45048445.fMDQidcC6G
Content-Disposition: attachment; filename="Making a raspbian.org style kernel.txt"
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Making a raspbian.org style kernel

https://plugwash.raspbian.org/linux_3.18/ https://sourcearchive.raspbian.org/main/l/linux/

1: take the debdiff
2: filter out debian/patches using filterdiff
3: apply the filtered debdiff to a Debian source package for the correct major version
4: deal with any bits of the patch that failed to apply
5: update the settings in debian/update-rpi-patches
6: make debian/update-rpi-patches executable (since diff/patch don't preserve permissions)
7: run debian/update-rpi-patches
8: try and work out what new config settings are needed from diffing the two major versions in the rpf repo, edit debian/config/armhf/config.rpi (I think that is the name, I may be misremembering) accordingly
9: hack away at the package until it builds successfully
10: build the package
11: test the kernel actually boots, if not hack on things some more until it does

ad 1)
debdiff between the raspbian kernel package and the debian kernel package it's based on.
debdiff linux_3.18.5-1~exp1.dsc linux-3.18_3.18.5-1~exp1+rpi20.dsc > linux-3.18.debdiff
Obtained the linux_3.18.5-1~exp1.dsc file through snapshot.debian.org (http://snapshot.debian.org/archive/debian/20150208T160746Z/pool/main/l/linux/)
Besides the .dsc file you also need the .orig.tar.xz file and the .debian.tar.xz file

ad 2)
filterdiff -p1 -x 'debian/patches/*' linux-3.18.debdiff > linux-3.18.debdiff.filtered

ad 7)
oh another thing, update-rpi-patches will run much faster if you have a clone of the rpi kernel tree in a directory called linuxgit in the parent of the directory where you have the package source extracted
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--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On Tuesday, 25 October 2022 11:33:40 CEST Arnd Bergmann wrote:

IIUC, for the kernel, either compiler should be fine. The
documentation[0] for compiling the RPi Zero kernel seems to bear this
out - it even uses the "CROSS_COMPILE=arm-linux-gnueabihf-". If you've
got access to the hardware it should be easy to test before kicking off
the Debian kernel package build.

How can I test that? I'm not a C programmer and I thought that crashes due to arch differences would only manifest themselves under certain circumstances which could take a while to manifest.

That is correct: it's the same compiler backend, the only difference
between an arm-linux-gnuabihf- and an arm-linux-gnueabi- toolchain are
which CPU and floating pointing ABI are set when building with the
default flags. The kernel itself is always built as soft-float even
for armv7 using an armhf toolchain, and the CPU is always set to
the minimum configured target machine, so both compilers will produce
the same kernel binary.

So this means I *can* actually use the arm-linux-gnuabihf compiler* already available in the Debian archives? I did not expect that as I _assumed_ it
would make binaries for Debian's armhf architecture.

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--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On Tuesday, 25 October 2022 12:01:01 CEST Arnd Bergmann wrote:

I have a Zero W running Debian's armel kernel and I find that device to be annoyingly slow.
I also have a RPi 1 running raspbian.org's 4.9 kernel, which is a special kernel build by plugwash and compiled like the rest of raspbian.org packages, which I do not find (annoyingly) slow.

The difference between the two kernels is almost certainly unrelated
to the toolchain they are built with,

That surprises me as I thought that raspbian.org's effort (and reason for existing at all) was entirely based on that.

and entirely based on the kernel patches that are added on top of mainline
as well as the configuration.

If there is a huge difference, my first guess would be the CPU frequency scaling driver: if the CPU runs a different operating point, that
would have a much larger impact than anything the kernel itself
can do.

In https://salsa.debian.org/kernel-team/linux/-/merge_requests/381 I did
enable the needed components for that. I will try whether the performance governor makes a notable difference.
RPi 1 only has 1 frequency, but RPi 0 has 2.

Another obvious difference may be the GPU support

They are both used headlessly, so that should be irrelevant.
The RPi 0W is attached to my smart energy meter and the RPi 1 I essentially only use(d) for development purposes.

If you have a fast Raspbian kernel and a slow Debian kernel for
the same source version, can you take a look at the /boot/config-*
files, and the list of loaded kernel modules, to see if there
are any obvious differences?

Can `=m` vs `=y` have a (relevant) impact?
I will ofc compare them, but I have already looked (a while ago) at the config for obvious missing components and only found 1 which is now fixed: https://salsa.debian.org/kernel-team/linux/-/merge_requests/486

Cheers,
Diederik
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* Origin: fsxNet Usenet Gateway (21:1/5)