Re: Testing versatile kernel on Raspberry Pi?
On Mon, 2016-01-25 at 17:59 +0100, Sebastian Reichel wrote:
> Hi,
>
> On Mon, Jan 25, 2016 at 05:39:40PM +0100, Diederik de Haas wrote:
> > On Monday 25 January 2016 14:58:27 Ian Campbell wrote:
> > > > As I got the impression that support for the RPi was now
> present in
> > > > upstream and (therefor) the Debian kernels,
> > >
> > > The "therefor" won't happen automatically, someone will need to
> file a
> > > wishlist bug asking for the relevant options to be enabled in the
> Debian
> > > kernel configuration.
> > >
> > > For the RPi's with the newer CPU cores it makes clear sense to do
> that in
> > > the armhf/armmp kernel flavour (since it is the "multiplatform"
> flavour,
> > > and the only one we want to support).
> >
> > I'll give it a try, but first have to learn about the armmp stuff.
> >
> > Here is the default kernel configuration for the RPi 2:
> > https://github.com/raspberrypi/linux/blob/rpi-4.4.y/arch/arm/config
> s/bcm2709_defconfig
> > (which does not seem part of
> > https://sources.debian.net/src/linux/4.4-1~exp1/arch/arm/configs/)
>
> The kernel from the Raspberry Pi foundation and the mainline kernel
> have different config options, so that won't be of much use. Check
> mainline's arch/arm/configs/bcm2835_defconfig instead.
>
> > > For the RPi's with the older cores it wouldn't seem to make much
> sense to
> > > enable it in the armel/versatile flavour (because I can't see why
> it fits
> > > there, despite folks apparently adding it there), but equally I'm
> not sure
> > > we want to be adding new flavours to armel (which is essentially
> on the
> > > downward slope of the support lifecycle at this stage). Perhaps
> others
> > > around here feel differently though.
> >
> > Bummer for me as it won't solve the issue I hoped it would solve,
> but I'll try
> > other avenues for that. But still, thanks for clarifying :-)
>
> Another option would be adding RPi1 support to the armhf armmp
> kernel. I guess the benefits of ARMv7 vs ARMv6 is neglectable for
> the kernel (no floating point operations and Thumb2 should stay
> disabled because of errata 430973 on some older Cortex-A8s [i.e.
> on N900])
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.
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.
Ian.
> and one could use armel userland + armmp kernel from armhf.
>
> -- Sebastian
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