[U-Boot] [PATCH v3 0/6] Run-time configuration of U-Boot via a flat device tree (fdt)

[Jason]

Simon, Stephen,

On Tue, Oct 11, 2011 at 04:54:27PM -0700, Simon Glass wrote:
> Hi Stephen,
> 
> On Tue, Oct 11, 2011 at 4:37 PM, Stephen Warren <swarren at nvidia.com> wrote:
> > Simon Glass wrote at Tuesday, October 11, 2011 4:26 PM:
> > ...
> >> and add some defines to your board (only ARM is currently supported):
> >>
> >>  #define CONFIG_OF_CONTROL       (to enable run-time config control via fdt)
> >>  #define CONFIG_OF_EMBED or CONFIG_OF_SEPARATE
> >>  (either build the fdt blob into U-Boot, or create a separate u-boot.dtb
> >>   and u-boot-dtb.bin)
> >>  #define CONFIG_DEFAULT_DEVICE_TREE   "<your name>"
> >>  (to specify the name of the device tree file is
> >>   board/<vendor>/dts/<your name>.dts)
> >>
> >> Typically a CPU device tree include file is provided which defines all the
> >> devices available on that CPU/SOC, with each set to 'status = "disabled"'.
> >> Board device tree files should adjust only the devices they use, setting
> >> 'status = 'ok"' in each case, and leaving the existing devices alone and
> >> disabled.
...
> >
> > In the Linux kernel, things used to work exactly as described above, but
> > the kernel has switched to having no "status" properties in the SoC base
> > file (and hence everything defaults to enabled), with the per-board .dts
> > files set 'status = "disabled"' where desired. I imagine U-Boot should
> > follow the same practice.
> >
> > I forget the exact reason for this in the kernel; it may simply have been
> > due to precedent on PowerPC. Grant Likely would know the details.
> 
> Well it's going to create a bit of work for boards that use only a
> subset of these 30-peripheral SOCs, but perhaps the expectation is
> that you would be buying a simpler SOC if you didn't need all the
> features.

I imagine u-boot's methodology of loading drivers only as needed will
prevent the unnecessary initialization of 30 drivers which are default
'status = "enabled";'.  Or, am I missing something?

thx,

Jason.