[Buildroot] [PATCH 5/5 v2] configs: add a DT-enabled Raspberry Pi defconfig

[Thomas Petazzoni <thomas.petazzoni@free-electrons.com>]

Hello,

On Sat, 10 Jan 2015 12:17:51 +0100, Thomas Petazzoni wrote:

> >   - we can not use the minimalist RPi defconfig bundled with the kernel,
> >     namely bcmrpi_quick_defconfig, because it is not DT-enabled, and
> >     sets CONFIG_ARM_PATCH_PHYS_VIRT to 'n', which prompts a value for
> >     CONFIG_PHYS_OFFSET, as it as no default for the bcm familly;
> > 
> >   - we have to use the 'default' but bloated bcmrpi_defconfig, which
> >     makes for a very fat kernel with lots of modules, and takes ages to
> >     build;
> > 
> >   - most importantly, the rpi-3.18.y branch is constantly rebased, so
> >     there is no guarantee that the sha1 I use today will still be usable
> >     in the long term. Using the name of hte branch is not better either.
> 
> Well, you could alternatively decide to have a custom kernel defconfig
> in board/raspberrypi/, which would be the same as bcmrpi_quick, with
> just the modifications you need for DT. Sure it means it will have to
> be updated from time to time, but hopefully at some point in the future
> the official bcmrpi_quick defconfig will have DT support enabled.

Another motivation would be to switch back to an internal toolchain.
Using an external toolchain here is quite inefficient: for an ARMv6
such as the RPi, we will fallback to the CodeSourcery toolchain, which
will generate ARMv5 soft-float code. Not nice for a VFP-using ARMv6.

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com