Re: Testing a OF Device Tree driver on a kernel using a board file.

[Grant Likely <grant.likely-s3s/WqlpOiPyB63q8FvJNQ@public.gmane.org>]

On Thu, Jun 27, 2013 at 9:22 PM, Mr. Robert G Palmer Jr.
<robert.palmer-yOrjPonjKN58UrSeD/g0lQ@public.gmane.org> wrote:
> I apologize up front if this is the wrong place for these questions.  I'm
> relatively new to the OF Device Tree.  If this is the wrong place, would
> someone point me to the correct discussion location.
>
> 1. Is it possible to take an existing kernel build that uses a board file
> move only a small portion into a Device Tree.  I am working on converting a
> driver from supporting only the board file to supporting both the board file
> and the OF Device Tree.  Unfortunately, the only test platform I have with
> the appropriate hardware is a Nexus7 and I'm using the Cyanogenmod build.
> This uses (or at least appears to use) a board file for the Nexus7.  Is it
> possible to write a small Device Tree description for only the driver I am
> working on?  Where would this device tree file be placed? How would I
> include it in the build? Any assistance and/or pointers would be
> appreciated.

Yes. Enable CONFIG_OF and add a dt_compat pointer to the existing
nexus7 MACHINE_START() stanze. Then a trivial device tree with a
top-level compatible property that matches something in the dt_compat
table can be used to boot the platform.

arch/arm/mach-versatile/versatile_dt.c shows an example.

> 2. Are there any suggestions or hints for searching for OF Device Tree
> information.  The term "device tree" is used pervasively in the linux code
> and various projects to refer to source branches of a particular device type
> rather than the OF Device Tree.  This makes it extremely difficult to
> isolate applicable answers.

This link is useful:
http://devicetree.org/Device_Tree_Usage

Also, look at the files in Documentation/devicetree in the Linux kernel.

g.