On 03/06/18 04:30, Geert Uytterhoeven wrote:
> Hi David,
> On Tue, Mar 6, 2018 at 4:54 AM, David Gibson
> <da...@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.l...@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 <da...@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 <da...@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 in the thread that Geert was responding to when he
created this thread.

(Laurent -- no need to worry about this for your current series.
Converting your dts files will be an easy task to do in a future
kernel version -- remind me if I forget to send a patch.)


> Note that while the dtc part applies on the in-kernel copy of dtc, it
> doesn't work there: "&{/}" behaves the same as "/" (i.e. no overlay
> fragment is generated), but "&{/foo}" does create the overlay fragment.
> Merging in Rob's for-next branch to upgrade Linux' copy of dtc fixes that.
> Thanks a lot!
> Converting my remaining overlay fragments to sugar syntax...
> Gr{oetje,eeting}s,
>                         Geert
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- 
> ge...@linux-m68k.org
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like 
> that.
>                                 -- Linus Torvalds
> .

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