Overlay sugar syntax (was: Re: [PATCH v6 3/4] drm: rcar-du: Fix legacy DT to create LVDS encoder nodes)
David Gibson
david at gibson.dropbear.id.au
Wed Mar 7 02:30:31 UTC 2018
On Tue, Mar 06, 2018 at 01:40:20PM -0800, Frank Rowand wrote:
> On 03/06/18 11:51, Frank Rowand wrote:
> > On 03/06/18 04:30, Geert Uytterhoeven wrote:
> >> Hi David,
> >>
> >> On Tue, Mar 6, 2018 at 4:54 AM, David Gibson
> >> <david at gibson.dropbear.id.au> wrote:
> >>> On Fri, Feb 23, 2018 at 09:05:24AM +0100, Geert Uytterhoeven wrote:
> >>>> On Fri, Feb 23, 2018 at 3:38 AM, Frank Rowand <frowand.list at gmail.com> wrote:
> >>>>> I was hoping to be able to convert the .dts files to use sugar syntax
> >>>>> instead of hand coding the fragment nodes, but for this specific set
> >>>>> of files I failed, since the labels that would have been required do
> >>>>> not already exist in the base .dts files that that overlays would be
> >>>>> applied against.
> >>>>
> >>>> Indeed, hence the fixup overlays use "target-path".
> >>>>
> >>>> BTW, is there any specific reason there is no sugar syntax support in dtc
> >>>> for absolute target paths? I guess to prevent adding stuff to a random
> >>>> existing node, and to encourage people to use a "connector" API defined in
> >>>> term of labels?
> >>>
> >>> Only because it hasn't been implemented. Using &{/whatever} should
> >>> IMO generate a target-path and the fact it doesn't is a bug.
> >>>
> >>>> I'm also in the process of converting my collection of DT overlays to sugar
> >>>> syntax, and lack of support for "target-path" is the sole thing that holds
> >>>> me back from completing this. So for now I use a mix of sugar and
> >>>> traditional overlay syntax.
> >>>>
> >>>> In particular, I need "target-path" for two things:
> >>>> 1. To refer to the root node, for adding devices that should live at
> >>>> (a board subnode of) the root node, like:
> >>>> - devices connected to GPIO controllers provided by other base or
> >>>> overlay devices (e.g. LEDs, displays, buttons, ...),
> >>>> - clock providers for other overlays devices (e.g. fixed-clock).
> >>
> >>>> The former is the real blocker for me.
> >>
> >>> Below is draft patch adding target-path support. The pretty minimal
> >>> test examples do include a case using &{/}
> >>>
> >>> From 8f1b35f88395adea01ce1100c5faa27dacbc8410 Mon Sep 17 00:00:00 2001
> >>> From: David Gibson <david at gibson.dropbear.id.au>
> >>> Date: Tue, 6 Mar 2018 13:27:53 +1100
> >>> Subject: [PATCH] Correct overlay syntactic sugar for generating target-path
> >>> fragments
> >>>
> >>> We've recently added "syntactic sugar" support to generate runtime dtb
> >>> overlays using similar syntax to the compile time overlays we've had for
> >>> a while. This worked with the &label { ... } syntax, adjusting an existing
> >>> labelled node, but would fail with the &{/path} { ... } syntax attempting
> >>> to adjust an existing node referenced by its path.
> >>>
> >>> The previous code would always try to use the "target" property in the
> >>> output overlay, which needs to be fixed up, and __fixups__ can only encode
> >>> symbols, not paths, so the result could never work properly.
> >>>
> >>> This adds support for the &{/path} syntax for overlays, translating it into
> >>> the "target-path" encoding in the output. It also changes existing
> >>> behaviour a little because we now unconditionally one fragment for each
> >>> overlay section in the source. Previously we would only create a fragment
> >>> if we couldn't locally resolve the node referenced. We need this for
> >>> path references, because the path is supposed to be referencing something
> >>> in the (not yet known) base tree, rather than the overlay tree we are
> >>> working with now. In particular one useful case for path based overlays
> >>> is using &{/} - but the constructed overlay tree will always have a root
> >>> node, meaning that without the change that would attempt to resolve the
> >>> fragment locally, which is not what we want.
> >>>
> >>> Signed-off-by: David Gibson <david at gibson.dropbear.id.au>
> >>
> >> Thank you, seems to work fine on dtc.git.
> >
> > And the patched dtc works for a dts file that I was trying to convert
> > to sugar dts syntax
>
> < snip >
>
> I noticed that a space in "&{/}" is an error. I wanted to check whether
> that was deliberate, or that the patch wasn't fully complete yet.
That's essentially deliberate - it's not really related to this patch
at all. The patch just re-uses the existing syntax for a "path
reference". The whole thing is treated as a single token, hence, no
spaces.
It might be possible to change that, but it could introduce some
complications when the path reference syntax is used in other places.
So I'm disinclined to change it, unless there's a very strong reason
to.
> cat path_sugar_v1.dts
>
> $ nl -ba path_sugar_v1.dts
> 1
> 2 /dts-v1/;
> 3 /plugin/;
> 4 &{/} {
> 5 #address-cells = <2>;
> 6 #size-cells = <2>;
> 7
> 8 my_node at feb90000 {
> 9 compatible = "vendor,device";
> 10 reg = <0 0xfeb90000 0 0x1c>;
> 11
> 12 };
> 13
> 14 };
>
> $ dtc -O dts path_sugar_v1.dts
> /dts-v1/;
>
> / {
>
> fragment at 0 {
> target-path = [2f 00];
>
> __overlay__ {
> #address-cells = <0x2>;
> #size-cells = <0x2>;
>
> my_node at feb90000 {
> compatible = "vendor,device";
> reg = <0x0 0xfeb90000 0x0 0x1c>;
> };
> };
> };
> };
>
> $ nl -ba path_sugar_v2.dts
> 1
> 2 /dts-v1/;
> 3 /plugin/;
> 4 &{ / } {
> 5 #address-cells = <2>;
> 6 #size-cells = <2>;
> 7
> 8 my_node at feb90000 {
> 9 compatible = "vendor,device";
> 10 reg = <0 0xfeb90000 0 0x1c>;
> 11
> 12 };
> 13
> 14 };
>
> $ dtc -O dts path_sugar_v2.dts
> Error: path_sugar_v2.dts:4.1-2 syntax error
> FATAL ERROR: Unable to parse input tree
>
--
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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