Hello all,

On Wed, May 01, 2024 at 09:18:01PM +0000, Humphreys, Jonathan wrote:

Problem statement:

Device trees are in theory a pure description of the hardware, and since the hardware doesn't change, the device tree describing the hardware likewise never changes. With this, a device tree could then be burned into the hardware's ROM to be queried by software for hardware discovery.

I would like to add another use case that I do not see mentioned here.

In case of SoM (System On Module) the system can be designed in such a way that the firmware does not really need to know the complete hardware description, but only the hardware subset relevant for booting and the initial hardware configuration is required.

However the operating system would need the complete hardware description, that is made of a SoM plus a carrier/base board, to properly work.

From a life cycle point of view the firmware of the SoM is going to be available and written to the board before the actual whole hardware is even existing and I would not expect to force the SoM user to update/customize the firmware.

Francesco