ARM: rpi: save bootargs from VC FDT to vc.bootargs ...

When booting a Raspberry Pi, it is useful to extract bootargs from the
device tree that was created by the VideoCore firmware. These bootargs
contain for example settings for the framebuffer that the kernel needs
to properly set the video output.

This commit extracts the bootargs in the board initialization code and
saves them to the vc.bootargs global variable.

For example, a bootloader environment can then add the contents of this
variable to linux.bootargs.vc, which then gets included into the final
bootargs for the kernel using CONFIG_FLEXIBLE_BOOTARGS.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

ARM: rpi: save fdt that was passed from VideoCore ...

On Raspberry Pi, VideoCore firmware creates a device tree that contains
information about peripherals that were initialized by VideoCore based
on settings in config.txt. Normally this device tree is passed to the
Linux kernel via a pointer in the r2 register. A bootloader needs to
pass this device tree to the kernel, or some peripherals will not work
correctly.

Since the VideoCore device tree is not compatible with barebox, we can't
just pass it to barebox_arm_entry() as the internal barebox device tree.

This commit makes the prebootloader code copy the device tree from
VideoCore into a scrap RAM area just above the area reserved for the
bootloader. Board initialization code in the bootloader proper then
copies it into a file /vc.dtb. The bootloader environment is then free
to pass this file to the kernel at boot (e.g. via bootm -o).

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

doc: bcm283x: remove miniuart overlay instruction ...

Since we now use the miniuart on the raspberry pi 3, the miniuart overlay is no
longer needed.

Signed-off-by: Rouven Czerwinski <r.czerwinski@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

doc: bcm283x: update documentation for Raspberry Pi ...

The old way does not seem to work for RPi 3, as the UART pins are
mapped differently and the NOOBS bootcode does not seem to read a
config.txt.

Signed-off-by: Roland Hieber <r.hieber@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Documentation: add Raspberry Pi barebox mini-howto ...

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>