Driver model currently only operates after relocation is complete. In this
state U-Boot typically has a small amount of memory available. In adding
support for driver model prior to relocation we must try to use as little
memory as possible.

In addition, on some machines the memory has not be inited and/or the CPU
is not running at full speed or the data cache is off. These can reduce
execution performance, so the less initialisation that is done before
relocation the better.

An immediately-obvious improvement is to only initialise drivers which are
actually going to be used before relocation. On many boards the only such
driver is a serial UART, so this provides a very large potential benefit.

Allow drivers to mark themselves as 'pre-reloc' which means that they will
be initialised prior to relocation. This can be done either with a driver
flag or with a 'dm,pre-reloc' device tree property.

To support this, the various dm scanning function now take a 'pre_reloc_only'
parameter which indicates that only drivers marked pre-reloc should be
bound.
Signed-off-by: NSimon Glass <sjg@chromium.org>

The lifecycle of a device is an important part of driver model. Add to the
existing documentation and clarify it.
Reported-by: NJon Loeliger <jdl@jdl.com>
Signed-off-by: NSimon Glass <sjg@chromium.org>

It is best to avoid having any occurence of 'struct device' in driver
model, so rename to achieve this.
Signed-off-by: NSimon Glass <sjg@chromium.org>

Signed-off-by: NChris Packham <judge.packham@gmail.com>

using UBI and DM together leads in compiler error, as
both define a "struct device", so rename "struct device"
in include/dm/device.h to "struct udevice", as we use
linux code (MTD/UBI/UBIFS some USB code,...) and cannot
change the linux "struct device"
Signed-off-by: NHeiko Schocher <hs@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Cc: Marek Vasut <marex@denx.de>

This adds a README to help with understanding of this series.
Signed-off-by: NSimon Glass <sjg@chromium.org>