Re: [PATCH v2 04/18] arm64: dts: m3ulcb-kf: initial device tree

[Pantelis Antoniou <pantelis.antoniou-OWPKS81ov/FWk0Htik3J/w@public.gmane.org>]

Hi Geert,

On Wed, 2017-09-20 at 14:32 +0200, Geert Uytterhoeven wrote:
> Hi Vladimir,
> 
> [CC Pantelis]
> 
> On Thu, Sep 14, 2017 at 4:18 PM, Vladimir Barinov
> <vladimir.barinov-M4DtvfQ/ZS1MRgGoP+s0PdBPR1lH4CV8@public.gmane.org> wrote:
> > Add the initial device tree for the M3ULCB with Kingfisher extension
> > infotainment board.
> >
> > Signed-off-by: Vladimir Barinov <vladimir.barinov-M4DtvfQ/ZS1MRgGoP+s0PdBPR1lH4CV8@public.gmane.org>
> > ---
> > Changes in version 2:
> > - added own compatible value "shimafuji,kingfisher"
> 
> Reviewed-by: Geert Uytterhoeven <geert+renesas-gXvu3+zWzMSzQB+pC5nmwQ@public.gmane.org>
> 
> Some food for thought below...
> 
> > --- /dev/null
> > +++ b/arch/arm64/boot/dts/renesas/r8a7796-m3ulcb-kf.dts
> > @@ -0,0 +1,19 @@
> > +/*
> > + * Device Tree Source for the M3ULCB Kingfisher board
> > + *
> > + * Copyright (C) 2017 Renesas Electronics Corp.
> > + * Copyright (C) 2017 Cogent Embedded, Inc.
> > + *
> > + * This file is licensed under the terms of the GNU General Public License
> > + * version 2.  This program is licensed "as is" without any warranty of any
> > + * kind, whether express or implied.
> > + */
> > +
> > +#include "r8a7796-m3ulcb.dts"
> 
> Ideally, we don't include *.dts files, only *.dtsi.
> But I don't see a better immediate solution.
> 
> > +#include "ulcb-kf.dtsi"
> 
> As the Kingfisher is actually an expansion board for H3ULCB (with R-Car H3
> ES1.1 and ES2.0) and M3ULCB (with R-Car M3-W), turning ulcb-kf.dtsi into a
> DT overlay would make sense.
> That would also solve the issue of the 3 extra DTSes needed for all possible
> combinations of ULCB and Kingfisher (r8a7795-es1-h3ulcb-kf.dts,
> r8a7795-h3ulcb-kf.dts, r8a7796-h3ulcb-kf.dts (perhaps more to follow?)).
> 
> But that's too premature, without upstream support for the easy loading of
> DT overlays.
> 

Sigh, yes.

> > +/ {
> > +       model = "Renesas M3ULCB Kingfisher board based on r8a7796";
> > +       compatible = "shimafuji,kingfisher", "renesas,m3ulcb",
> > +                    "renesas,r8a7796";
> > +};
> 
> And how to support from an overlay the addition of "shimafuji,kingfisher" to
> (not replacement of!) the main compatible value?
> 

You can hack something in DT but it will be gross indeed.

Ideally you'd want a += operator, but it's going to take a lot of
changes starting from DTB blob format.

In yaml we could easily do this with an append tag type

compatible: [ "renesas,m3ulcb", "renesas,r8a7796" ]

compatible: !append "shimafuji,kingfisher"

Are you going to be at ELCE? I have a bunch of thing to ask you about
your DT usage patterns.

Regards

-- Pantelis

> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.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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