On Tue, Apr 5, 2016 at 5:03 PM, Pantelis Antoniou pantelis.antoniou@konsulko.com wrote:
Hi Maxime,
On Apr 4, 2016, at 11:25 , Maxime Ripard maxime.ripard@free-electrons.com wrote:
The device tree overlays are a good way to deal with user-modifyable boards or boards with some kind of an expansion mechanism where we can easily plug new board in (like the BBB or the raspberry pi).
However, so far, the usual mechanism to deal with it was to have in Linux some driver detecting the expansion boards plugged in and then request these overlays using the firmware interface.
That works in most cases, but in some cases, you might want to have the overlays applied before the userspace comes in. Either because the new board requires some kind of an early initialization, or because your root filesystem is accessed through that expansion board.
The easiest solution in such a case is to simply have the component before Linux applying that overlay, removing all these drawbacks.
[...]
diff --git a/cmd/fdt_overlay.c b/cmd/fdt_overlay.c
This looks it’s general libfdt code. It should end up in libfdt/ so that others can use it, and eventually be pushed upstream.
+1. It really needs to go into libfdt first to avoid any re-licensing issues.
Another option which Grant has suggested would be to extend the FDT format to include overlays as a whole. Then the kernel can apply them during unflattening. This would simplify things on the bootloader side.
Rob