linux-kernel - Re: [PATCH v3 07/10] riscv: boot: dts: r9a07g043: Add placeholder nodes

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Date:   Tue, 20 Sep 2022 14:17:50 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Conor Dooley <mail@...chuod.ie>
Cc:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>,
        Conor.Dooley@...rochip.com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, paul.walmsley@...ive.com,
        palmer@...belt.com, aou@...s.berkeley.edu, heiko@...ech.de,
        atishp@...osinc.com, devicetree@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-renesas-soc@...r.kernel.org,
        linux-kernel@...r.kernel.org, biju.das.jz@...renesas.com,
        prabhakar.mahadev-lad.rj@...renesas.com
Subject: Re: [PATCH v3 07/10] riscv: boot: dts: r9a07g043: Add placeholder nodes

Hi Conor,

On Fri, Sep 16, 2022 at 12:40 AM Conor Dooley <mail@...chuod.ie> wrote:
> On 15/09/2022 23:26, Lad, Prabhakar wrote:
> > On Thu, Sep 15, 2022 at 10:36 PM <Conor.Dooley@...rochip.com> wrote:
> >> On 15/09/2022 19:15, Prabhakar wrote:
> >>> riscv: boot: dts: r9a07g043: Add placeholder nodes
> >>> From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> >>> Add empty placeholder nodes to RZ/Five (R9A07G043) SoC DTSI.
> >> Can you explain why do you need placeholder nodes for this and
> >> cannot just directly include the other dtsis?
> >>
> > Since the RZ/G2UL SoC is ARM64 where it has a GIC and on RZ/Five SoC
> > we have PLIC for interrupts. Also the interrupt numbering for RZ/Five
> > SoC differs from RZ/G2UL SoC hence we are not directly using the
> > RZ/G2UL SoC DTSI [0].
> >
> > [0] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/boot/dts/renesas/r9a07g043.dtsi?h=v6.0-rc5
> >
> > For the RZ/Five SMARC EVK I am re-using the below files [1] (SoM) and
> > [2] (Carrier board) as the RZ/Five SMARC EVK is pin compatible.  Since
> > I am re-using these when trying to compile the RZ/Five DTB I get
> > compilation errors since the nodes dont exist (and there is no way
> > currently we can delete the node reference when the actual node itself
> > isn't present) hence these place holders.
> >
> > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/boot/dts/renesas/rzg2ul-smarc-som.dtsi?h=v6.0-rc5
> > [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/boot/dts/renesas/rzg2ul-smarc.dtsi?h=v6.0-rc5
>
> If this method is acceptable to Geert, this explanation 100% needs to
> go into the commit message.

We've been using these placeholders a lot in Renesas SoC-specific
.dtsi files, as they allow us to introduce gradually support for a new SoC
that is mounted on an existing PCB, and thus shares a board-specific
.dtsi file.  Hence I'm fine with this.

However, I think more properties can be dropped from the placeholders.
There is no need to have e.g. 'reg-names' and 'status = "disabled"'
(there is no compatible value, so no matching is done).

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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