Re: [PATCH v3 0/2] Add capability to append to property

On Thu, Dec 26, 2024 at 7:54 AM David Gibson
<[email protected]> wrote:
> On Fri, Dec 20, 2024 at 09:00:14PM +0530, Ayush Singh wrote:
> > On 16/12/24 11:39, David Gibson wrote:
> > > On Tue, Dec 10, 2024 at 04:34:17PM +0100, Andreas Gnau wrote:
> > > > If we add /append-property/, why not add /prepend-property/ as well? This is
> > > > not only "nice for consistency", but it would also enable solving a problem
> > > > where SoC compatible strings from dtsi [1] need to be repeated in board dts
> > > > [2], because one cannot prepend to an existing property.
> > > >
> > > > ```
> > > > dts-v1/;
> > > > / {
> > > >   compatible = "soc-vendor,soc1234";
> > > > };
> > > >
> > > > / {
> > > >   /prepend-property/ compatible = "board-vendor,board-xyz";
> > > > };
> > > > ```
> > > >
> > > > What do you think?
> > > So, this kind of demonstrates why I don't love /append-property/ as a
> > > proposed syntax.  The way I'd prefer to do this, ideally, is to allow
> > > properties to be described as expressions.  We already have integer
> > > expressions that can be used in < > context, but I had intended to
> > > extent to string and bytestring expressions - but I've never had the
> > > time to implement that.
> > >
> > > Under that proposal, I'd expect appending to look something like:
> > >     str-prop = /previous-value/, "1";
> > >
> > > Prepending,
> > >     str-prop = "1", /previous-value/;
> > >
> > > .. and you could do both at once in the obvious way.
> > >
> > > The downside, of course, is that this is a much more complicated
> > > proposal to implement.  Parsing that syntax isn't too hard, but I
> > > think doing it sensibly will need some structural changes in order to
> > > evaluate property values as expressions, rather than simply
> > > constructing the properties directly left to right.  In particular the
> > > interactions between expression syntax and within-property labels (and
> > > other markers) could be fiddly to get right.
> >
> > Do you wish to allow `/previous-value/` to be repeated in the same property?
> > Something like this:
> >
> >     str-prop = "1", /previous-value/, "2", /previous-value/, "3";
>
> Yes, I'd expect that to work.  Note that I don't particularly like the
> name "/previous-value/" - that was just an example to demonstrate what
> I had in mind.  If anyone can think of a better or more succinct name
> for this, please suggest it.

Something like "/./"? (dot is also used in assembler for the current address)
So e.g.

    str-prop = "1", /./, "2", /./, "3";

Or would that be too short? "/orig/"?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected]

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