From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Gibson <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org>
Subject: Re: dtc 1.6.0 overlay full-path reference in array produces broken
 property names
Date: Mon, 1 Nov 2021 17:19:20 +1100
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References: <20210927140456.4e45f05b@gmail.com>
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To: Vincent Pelletier <plr.vincent-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
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On Mon, Sep 27, 2021 at 02:04:56PM +0000, Vincent Pelletier wrote:
> (please keep me cc'ed in replies)
>=20
> Hello,
>=20
> I suspect this may be a dtc bug, but I am not too familiar with
> devicetree specs to tell.
>=20
> Here is a simplified example reproducing this issue:
>=20
> (SNIP)
> /dts-v1/;
> /plugin/;
>=20
> / {
>   compatible =3D "foo";
> };
>=20
> &{/soc/gpio@7e200000} {
>     status =3D "okay";
> };
>=20
> &{/soc/spi@7e204000} {
>     cs-gpios =3D <&{/soc/gpio@7e200000} 8 0x01>;
> };
> (SNIP)
>=20
> This code builds fine:
>   $ dtc -I dts -O dtb -o test.dtbo test.dts
>   $
> But then when disassembling the output, I get:
>   $ dtc -I dtb -O dts test.dtbo
>   <stdout>: ERROR (property_name_chars): /__fixups__:/soc/gpio@7e200000: =
Bad character '/' in property name
>   ERROR: Input tree has errors, aborting (use -f to force output)
> And forcing output:
>   $ dtc -I dtb -O dts -f test.dtbo
>   <stdout>: ERROR (property_name_chars): /__fixups__:/soc/gpio@7e200000: =
Bad character '/' in property name
>   Warning: Input tree has errors, output forced
>   /dts-v1/;
>=20
>   / {
>           compatible =3D "foo";
>=20
>           fragment@0 {
>                   target-path =3D "/soc/gpio@7e200000";
>=20
>                   __overlay__ {
>                           status =3D "okay";
>                   };
>           };
>=20
>           fragment@1 {
>                   target-path =3D "/soc/spi@7e204000";
>=20
>                   __overlay__ {
>                           cs-gpios =3D <0xffffffff 0x08 0x01>;
>                   };
>           };
>=20
>           __fixups__ {
>                   /soc/gpio@7e200000 =3D "/fragment@1/__overlay__:cs-gpio=
s:0";
>           };
>   };
>=20
> Indeed, the node in __fixups__ has an invalid name.
>=20
> I suspect this is uncommon because:
> - it probably only occurs in overlays and not in self-contained trees,
>   as a self-contained tree would likely produce an internal phandle and
>   never store the full path anywhere.
> - ...which does not attach to labels but full paths
>   Labels being (probably ?) valid node names, they would avoid the issue.
> - ...in arrays
>   In a node overlay, the full path ends up as a quoted string, not as a
>   name, so it is safe.
>=20
> Is this a dtc bug ?

I've looked at this again and... not really.

Unfortunately, such a reference can't work given the specification of
the overlay format.  The property name in fixups is the target of the
reference, which works fine for labels, but will necessarily result in
an invalid property name for path references.

dtc should, of course, have a less ugly failure mode.

--=20
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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