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Re: armhf kernels on arm64 hardware

On Fri, Jul 15, 2022 at 6:13 PM Wookey <wookey@wookware.org> wrote:
> On 2022-07-15 18:42 +0800, Paul Wise wrote:
> > On Fri, 2022-07-15 at 12:04 +0200, Arnd Bergmann wrote:
> On the other hand, if the armhf kernel does work on RPi4 with a few
> config options, and there is an actual use case, then the question is
> what is the downside of enabling the config options?
> Does this only work for the RPi4, or does it enable/prevent 32-bit
> kernels on other 64-bit machines?

The bug report was only about a missing driver for the Raspberry Pi 4,
enabling the driver has no effect on other machines besides making the
kernel slightly bigger, or adding another kernel module if it can be
modular (most PCI host drivers are traditionally built-in, though that is
not strictly necessary).

> Do i386 kernels work on amd64 machines?
> Sounds like something that might be worth discussion at debconf next week. I'll mention it in the talk.

It is generally possible to run 32-bit kernels on 64-bit hardware on x86,
some armv8 and mips, but there are a lot of downsides. On powerpc,
sparc, riscv, and newer armv8/v9, one has to run a 64-bit kernel.

Traditionally you'd only have a 64-bit kernel but 32-bit user space, at
least on powerpc, pa-risc and sparc.

I think x86 and arm are the odd ones out here, because Debian has
never shipped a 64-bit kernel packaged as a 32-bit .deb file here,
though at the moment mipsel is the only one that ships with
64-bit kernel by default.


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