Re: [RFC] dt: add of_platform_bus_snoop() which attaches nodes to devices

On Mon, Jan 31, 2011 at 3:01 PM, Grant Likely [off-list ref] w=
rote:

This patch implements an alternate method for using device tree data
for populating machine device registration. =A0Traditionally, board
support has directly generated and registered devices based on nodes
in the device tree. =A0The board support code starts at the root of the
tree and begins allocating devices for each device node it finds.
Similarly, bus drivers (i2c, spi, etc.) use their child nodes to
register child devices. =A0This model can be seen in almost all the power=

pc

board ports (arch/powerpc/platforms/*).

However, for many of the ARM SoCs, there already exists complete board
support for many SoCs that have their own code for registering the
basic set of platform devices with non-trivial dependencies on clock
structure and machine specific platform code. =A0While starting at the
base of the tree and working up is certainly possible, it requires
modifying a lot of machine support code to get it working.

Instead, this patch provides an alternate approach. =A0Instead of
starting at the root of the tree and working up, this patch allows the
SoC support code to register its standard set of platform devices in
the normal way. =A0However, it also registers a platform_bus notifier
function which compares platform_device registrations with data in the
device tree. =A0Whenever it finds a matching node, it increments the
node reference count and assigns it to the device's of_node pointer so
that it is available for the device driver to use and bind against.
For example, an spi master driver would have access to the spi node
which contains information about all the spi slaves on the bus.

One more note.  It might also be a good idea to do something like this
for the PCI and AMBA buses.  I've not yet looked at how much code
could be made common for implementing that.

g.