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Re: Testing versatile kernel on Raspberry Pi?



On Tuesday 26 January 2016 08:24:16 Ian Campbell wrote:
> The Debian armhf kernels do not have support for ARMv6 enabled. AIUI
> moving to a v6+v7 capable kernel, other than muddying the waters WRT
> what "armhf" means, would also mean falling back to ARMv6 features only
> missing out on ARMv7 additions like improvements to SMP barriers and
> atomic operations. I don't think we'd want to do that.

Nor would I want that.
My assumption was that the new Debian versatile kernel would/could work 
(pretty much) unmodified on a RPi 1 and 2. But I now know that that assumption 
was wrong. I never wanted or intended for Debian to change something as major 
as their, properly documented, definition of armhf.

> IMHO RPi1 is best supported by Raspbian, or if people really want it in
> Debian then by armel, but not by an armhf+armel hybrid which involves
> supporting v6 in some way on armhf.

That Debian's armhf and armel didn't make full use of the RPi hardware is the 
whole reason that Raspbian was born and there's nothing wrong with that and it 
works fine.
The only downside to the kernels used (and made by the RPF) on the RPi is that 
it doesn't have a linux-headers-* package, but there are ways around that too 
[1].

As for getting the armmp kernel working on the Pi 2, I'll better leave that to 
the RPF kernel folks as they can (as opposed to me) asses whether that is 
feasible and/or desirable. 
When I compared "config ARCH_MULTIPLATFORM" [2] with what is enabled in the RPF 
kernels, most of them were off. I can look up the definition of those settings, 
but I (very likely) would still have no clue whether enabling them would have 
any adverse side effects. 
While I love the enthusiasm and help I've gotten here, I think it's better and 
safer to acknowledge that this is outside my area of expertise.

Cheers,
  Diederik

[1] https://github.com/diederikdehaas/cknow.org/blob/master/rpi/compile-kernel-module-on-raspberrypi.md
[2] https://sources.debian.net/src/linux/4.4-1~exp1/arch/arm/Kconfig/#L320

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