Re: [RFC] using dt overlays: how to? today?

Hi Ludovic,

On Jan 22, 2015, at 17:02 , Ludovic Desroches [off-list ref] wrote:

Hi,

I have assisted to Pantelis' talk about device tree and overlays at ELCE
2014. Since the patch 'Introduce DT overlay support' is now part of the
mainline, I wanted to have a look about it and to use it for our boards.

Excellent.

Firstly, this is what I want to achieve by using this feature:
- manage several revisions of our boards
- manage modules we can plug on the board, mainly display modules
 (resistive or capacitive one)
- manage cpu modules plug on the motherboard
- I would like to have all this stuff in the kernel. I don't want a
 dependency on the bootloader or the user space.

That’s awesome; that’s exactly what I want to use it for. Maybe this thing
can be used by others as well ;)

At the moment, we have many dts files to manage these cases (not all are
in mainline). It is becoming a pain.

Tell me about it.

I wanted to see if we can use device tree fragments as it seems to be
closed to be achieved when I had assisted to the talk. I have found a
thread about 'DT-Overlay configfs interface'
(http://thread.gmane.org/gmane.linux.drivers.devicetree/101871), there
are still discussions about security concerns, so it may not be included
quickly. I have also found an interesting thread about cape manager for
Beaglebone (http://thread.gmane.org/gmane.linux.documentation/8279) but
there is no more activity on it, is it canceled or is there a new topic
I have missed?

Here are my questions:
- Is it acceptable to manage device tree fragments with a driver such as
 the cape manager? Or at an other place in the kernel such as
arch/arm/mach-at91/board-dt-sama5.c for example?
- Is it possible to get access to eeprom from the kernel? Pantelis did
 an interface to access it through i2c but it seems it was not
accepted. In my case, it will be through the one wire interface.

Thanks for sharing your opinion about this or redirecting me to a
similar thread.

I’m waiting for 3.19 to go out and I’ll address everything you described
above.

Feel free to post specific requirement about your use cases, and I’ll try
to address them.

Ludovic
—

Regards

— Pantelis

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