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

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

[Mr. Robert G Palmer Jr.]

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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.

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.

Thank you,
-- 
Robert G. Palmer, Jr.
President
Ingenutec, LLC
Mentor for HVA RoHAWKtics, FIRST Robotics Team 3824
865-405-5695
robert.palmer-yOrjPonjKN58UrSeD/g0lQ@public.gmane.org
www.ingenutec.com




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

[Grant Likely]

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.