[PATCH] fdtdec: fdtdec_get_aliases_highest_id: skip aliases to disabled nodes

[Tim Harvey]

On Thu, Apr 29, 2021 at 9:10 AM Simon Glass <sjg at chromium.org> wrote:
>
> Hi Tim,
>
> On Fri, 16 Apr 2021 at 14:30, Tim Harvey <tharvey at gateworks.com> wrote:
> >
> > When looking for an alias with the highest id skip aliases for nodes
> > that are disabled.
> >
> > Signed-off-by: Tim Harvey <tharvey at gateworks.com>
> > ---
> >  lib/fdtdec.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/lib/fdtdec.c b/lib/fdtdec.c
> > index 864589193b..d47195525a 100644
> > --- a/lib/fdtdec.c
> > +++ b/lib/fdtdec.c
> > @@ -546,6 +546,8 @@ int fdtdec_get_alias_highest_id(const void *blob, const char *base)
> >                 if (*prop != '/' || prop[len - 1] ||
> >                     strncmp(name, base, base_len))
> >                         continue;
> > +               if (!fdtdec_get_is_enabled(blob, fdt_path_offset(blob, prop)))
> > +                       continue;
>
> We really can't do this here. It is quite an expensive operation to
> locate the node for a path.
>
> Why is this needed? It seems odd to have an alias pointing to a disabled device.
>

Simon,

The issue I ran into here was with an imx6 based board that does not
use the FEC ethernet on the SoC. In this case imx6qdl.dtsi delcares an
alias 'thernet0 = &fec' yet the fec node is not enabled. However
because fdtdec_get_alias_highest_id does not skip this alias to a
disabled device any enumerated ethernet devices get an index of 1
instead of 0 which is incorrect and causes the mac addresses to be
misaligned.

In general it is just wrong to reserve id's for disabled devices.

Tim