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Re: Testing versatile kernel on Raspberry Pi?

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On Tue, Jan 26, 2016 at 08:24:16AM +0000, Ian Campbell wrote:
> 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,

An amd64 kernel can also boot i386, so imho kernel is always
special.

> 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.

Ok, I assumed the kernel was capable of checking runtime if
it can use those features. Never mind then.

> 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.

I had a few RPi1s running with armel. For simple tasks (e.g.
network2gpio or i2c) it's more than enough. I wonder if an armel
-armmp kernel would be worth the trouble. We currently have the
following armel kernel targets:

-kirkwood  (multiplatform support since v3.14 (ba5a37e521942))
-orion5x   (multiplatform support since v4.5 [0])
-versatile (DT only since v4.5 [0])

So maybe switch to -armv5 and -armv6 multiplatform kernels from
v4.5+?

-armv5     kirkwood + orion5x + versatile
-armv6     bcm2036

[0] http://lkml.iu.edu/hypermail/linux/kernel/1601.2/03005.html

-- Sebastian

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Thread

Testing versatile kernel on Raspberry Pi? Diederik de Haas <didi.debian@cknow.org> - 2016-01-16 03:30 +0100
  Re: Testing versatile kernel on Raspberry Pi? Ian Campbell <ijc@debian.org> - 2016-01-25 14:30 +0100
    Re: Testing versatile kernel on Raspberry Pi? Diederik de Haas <didi.debian@cknow.org> - 2016-01-25 15:50 +0100
      Re: Testing versatile kernel on Raspberry Pi? Ben Hutchings <ben@decadent.org.uk> - 2016-01-25 16:00 +0100
        Re: Testing versatile kernel on Raspberry Pi? Ian Campbell <ijc@debian.org> - 2016-01-25 16:10 +0100
          Re: Testing versatile kernel on Raspberry Pi? Diederik de Haas <didi.debian@cknow.org> - 2016-01-25 17:30 +0100
      Re: Testing versatile kernel on Raspberry Pi? Ian Campbell <ijc@debian.org> - 2016-01-25 16:00 +0100
        Re: Testing versatile kernel on Raspberry Pi? Diederik de Haas <didi.debian@cknow.org> - 2016-01-25 17:40 +0100
          Re: Testing versatile kernel on Raspberry Pi? Sebastian Reichel <sre@debian.org> - 2016-01-25 18:10 +0100
            Re: Testing versatile kernel on Raspberry Pi? Ian Campbell <ijc@debian.org> - 2016-01-26 09:30 +0100
              Re: Testing versatile kernel on Raspberry Pi? Sebastian Reichel <sre@debian.org> - 2016-01-26 14:00 +0100
                Re: Testing versatile kernel on Raspberry Pi? Ben Hutchings <ben@decadent.org.uk> - 2016-01-26 14:50 +0100
                Re: Testing versatile kernel on Raspberry Pi? Ben Hutchings <ben@decadent.org.uk> - 2016-01-27 18:50 +0100
                Re: Testing versatile kernel on Raspberry Pi? Sebastian Reichel <sre@debian.org> - 2016-01-27 19:20 +0100
                Re: Testing versatile kernel on Raspberry Pi? Ben Hutchings <ben@decadent.org.uk> - 2016-01-27 19:30 +0100
                Re: Testing versatile kernel on Raspberry Pi? Sebastian Reichel <sre@debian.org> - 2016-01-27 21:00 +0100
              Re: Testing versatile kernel on Raspberry Pi? Diederik de Haas <didi.debian@cknow.org> - 2016-01-26 16:20 +0100
            Re: Testing versatile kernel on Raspberry Pi? Ian Campbell <ijc@hellion.org.uk> - 2016-01-26 10:50 +0100

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