Re: [PATCH 0/3 - V2] Introducing Device Tree Overlays

From: Guenter Roeck
Date: Wed Nov 06 2013 - 14:30:49 EST

On Wed, Nov 06, 2013 at 08:01:52PM +0100, Sebastian Andrzej Siewior wrote:
> On 05.11.13, Pantelis Antoniou wrote:
> > The following patchset introduces Device Tree overlays, a method
> > of dynamically altering the kernel's live Device Tree, along with
> > a generic interface to use it in a board agnostic manner.
> In case this has been discussed and I missed it: Why are we doing this?
> Isn't it possible to d o the overlay thingy in u-boot and pass a
> complete device tree to the kernel?
> Are you trying to do something like hotplug-PCI where the PCI card can
> be replaced at runtime?

At least that is our use case. u-boot doesn't know which cards are going to be
inserted at runtime. Even PCIe hotplug itself is insufficient, as the PCIe
configuration differs per card, and the cards support a variety of i2c devices
as well as other card specific devices such LEDs and multi-function FPGAs.

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