On Fri, Jul 01, 2016 at 01:59:58PM +0300, Pantelis Antoniou wrote:
> Hi Frank,
>
> Comments inline.
>
> > On Jul 1, 2016, at 03:02 , Frank Rowand <frowand.list@xxxxxxxxx> wrote:
> >
> > Hi All,
> >
> > I've been trying to wrap my head around what Pantelis and Rob have written
> > on the subject of a device tree representation of a connector for a
> > daughter board to connect to (eg a cape or a shield) and the representation
> > of the daughter board. (Or any other physically pluggable object.)
> >
> > After trying to make sense of what had been written (or presented via slides
> > at a conference - thanks Pantelis!), I decided to go back to first principals
> > of what we are trying to accomplish. I came up with some really simple bogus
> > examples to try to explain what my thought process is.
> >
> > To start with, assume that the device that will eventually be on a daughter
> > board is first soldered onto the main board. Then the device tree will
> > look like:
> >
> > $ cat board.dts
> > /dts-v1/;
> >
> > / {
> > #address-cells = < 1 >;
> > #size-cells = < 1 >;
> >
> > tree_1: soc@0 {
> > reg = <0x0 0x0>;
> >
> > spi_1: spi1 {
> > };
> > };
> >
> > };
> >
> > &spi_1 {
> > ethernet-switch@0 {
> > compatible = "micrel,ks8995m";
> > };
> > };
> >
> > #include "spi_codec.dtsi"
> >
> > $ cat spi_codec.dtsi
> > &spi_1 {
> > codec@1 {
> > compatible = "ti,tlv320aic26";
> > };
> > };
> >
> >
> > #----- codec chip on cape
> >
> > Then suppose I move the codec chip to a cape. Then I will have the same
> > exact .dts and .dtsi and everything still works.
> >
> >
> > @----- codec chip on cape, overlay
> >
> > If I want to use overlays, I only have to add the version and "/plugin/",
> > then use the '-@' flag for dtc (both for the previous board.dts and
> > this spi_codec_overlay.dts):
> >
> > $ cat spi_codec_overlay.dts
> > /dts-v1/;
> >
> > /plugin/;
> >
> > &spi_1 {
> > codec@1 {
> > compatible = "ti,tlv320aic26";
> > };
> > };
> >
>
> The correct form now for the /plugin/ declaration should be like
>
> /dts-v1/ /plugin/;
>
> The old method still works for backward compatibility.
>
> In fact with the new patches you don’t even /plugin/ since when
> compiling an overlay we can turn on the plugin flag by looking
> at the output type (dtbo).
I'd prefer to see the dtbo option go away however, in favour of the
/plugin/ flag.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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