The firmware uses tags in the kernel trailer to choose which dtb file
to load. Current firmware loads bcm2835-*.dtb if the '283x' tag is true,
otherwise it loads bcm270*.dtb. This scheme breaks if an image supports
multiple platforms.
This patch adds '270X' and '283X' tags to indicate support for RPi and
upstream platforms, respectively. '283x' (note lower case 'x') is left
for old firmware, and is only set if the image only supports upstream
builds.
The Raspberry Pi firmware looks for a trailer on the kernel image to
determine whether it was compiled with Device Tree support enabled.
If the firmware finds a kernel without this trailer, or which has a
trailer indicating that it isn't DT-capable, it disables DT support
and reverts to using ATAGs.
The mkknlimg utility adds that trailer, having first analysed the
image to look for signs of DT support and the kernel version string.
knlinfo displays the contents of the trailer in the given kernel image.
scripts/mkknlimg: Add support for ARCH_BCM2835
Add a new trailer field indicating whether this is an ARCH_BCM2835
build, as opposed to MACH_BCM2708/9. If the loader finds this flag
is set it changes the default base dtb file name from bcm270x...
to bcm283y...
Also update knlinfo to show the status of the field.
scripts/mkknlimg: Improve ARCH_BCM2835 detection
The board support code contains sufficient strings to be able to
distinguish 2708 vs. 2835 builds, so remove the check for
bcm2835-pm-wdt which could exist in either.
Also, since the canned configuration is no longer built in (it's
a module), remove the config string checking.
See: https://github.com/raspberrypi/linux/issues/1157
