On Sat, Jun 02, 2018 at 09:17:13PM +0000, Pascal Vizeli wrote: > diff --git a/Documentation/user/devicetree.rst b/Documentation/user/devicetree.rst > index 17934d86e..b2220997d 100644 > --- a/Documentation/user/devicetree.rst > +++ b/Documentation/user/devicetree.rst > @@ -21,7 +21,7 @@ The internal devicetree > ----------------------- > > The devicetree consulted by barebox plays a special role. It is referred to > -as the "internal devicetree." The barebox devicetree commands work on this > +as the "internal devicetree". The barebox devicetree commands work on this > devicetree. The devicetree source (DTS) files are kept in sync with the kernel DTS > files. As the FDT files are meant to be backward compatible, it should always be possible > to start a kernel with the barebox internal devicetree. However, since the barebox > @@ -83,3 +83,102 @@ you can exchange the internal devicetree during runtime using the > > oftree -f > oftree -l /new/dtb > + > +Devicetree overlays > +------------------- > + > +Since version 3.19, the Linux kernel supports applying "devicetree overlays" to > +its loaded device tree. This can be used to inform the kernel about additional > +non-discoverable devices after the system has booted, which is useful for modular > +boards and FPGAs. The details of the overlay format are specified in the Linux > +`kernel documentation <https://www.kernel.org/doc/Documentation/devicetree/overlay-notes.txt>`_ > +and an updated DTC is required to compile the overlays. > + > +The use cases for overlays in barebox are a bit different: > + > +* some of the modular devices are needed to boot Linux to userspace, but barebox > + can detect which module variant is connected > +* one of several parallel or LVDS displays (which use timing data from devicetree) > + can be connected to the SoC and should be used for boot messages > +* a generic Linux (distribution) kernel should be booted on a modular > + system and support additional hardware on modules > + > +barebox supports applying overlays in the internal devicetree was well using the > +:ref:`command_oftree` command with option ``-o``: > + > +.. code-block:: sh That highlighting looks weird with mixed languages. I suggest .. code-block:: none instead. (Ideally, this should also be used for all the other code blocks on that page, IMO ☺) - Roland > + > + $ ./barebox -d arch/sandbox/dts/sandbox.dtb -i arch/sandbox/dts/sandbox-overlay.dtbo > + add fd0 backed by file arch/sandbox/dts/sandbox-overlay.dtbo > + > + barebox 2015.02.0 #26 Wed Mar 4 09:41:19 CET 2015 > + ... > + barebox@barebox sandbox:/ of_dump > + ... > + dummy@0 { > + status = "disabled"; > + linux,phandle = <0x1>; > + phandle = <0x1>; > + }; > + dummy@1 { > + status = "disabled"; > + linux,phandle = <0x2>; > + phandle = <0x2>; > + }; > + __symbols__ { > + dummy0 = "/dummy@0"; > + dummy1 = "/dummy@1"; > + }; > + ... > + barebox@barebox sandbox:/ of_dump -f /dev/fd0 > + { > + fragment@0 { > + target = <0xdeadbeef>; > + __overlay__ { > + status = "okay"; > + child { > + compatible = "barebox,dummy"; > + }; > + }; > + }; > + fragment@1 { > + target = <0xdeadbeef>; > + __overlay__ { > + status = "okay"; > + child { > + compatible = "barebox,dummy"; > + }; > + }; > + }; > + __fixups__ { > + dummy0 = "/fragment@0:target:0"; > + dummy1 = "/fragment@1:target:0"; > + }; > + }; > + barebox@barebox sandbox:/ oftree -o /dev/fd0 > + barebox@barebox sandbox:/ of_dump > + ... > + dummy@0 { > + linux,phandle = <0x1>; > + phandle = <0x1>; > + status = "okay"; > + child { > + compatible = "barebox,dummy"; > + }; > + }; > + dummy@1 { > + linux,phandle = <0x2>; > + phandle = <0x2>; > + status = "okay"; > + child { > + compatible = "barebox,dummy"; > + }; > + }; > + __symbols__ { > + dummy0 = "/dummy@0"; > + dummy1 = "/dummy@1"; > + }; > + ... > + > +If you need to use a different base devicetree instead of the one compiled into > +barebox, it needs to be replaced as described in the previous section. [...] -- Roland Hieber | r.hieber@xxxxxxxxxxxxxx | Pengutronix e.K. | https://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim | Phone: +49-5121-206917-5086 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | _______________________________________________ barebox mailing list barebox@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/barebox
