linux-kernel - Re: [PATCH v5 1/6] dt-bindings: Add a binding for Mediatek SCP

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Date:   Mon, 4 Mar 2019 11:51:55 -0600
From:   Rob Herring <robh@...nel.org>
To:     Pi-Hsun Shih <pihsun@...omium.org>
Cc:     Erin Lo <erin.lo@...iatek.com>, Ohad Ben-Cohen <ohad@...ery.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "open list:REMOTE PROCESSOR (REMOTEPROC) SUBSYSTEM" 
        <linux-remoteproc@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 1/6] dt-bindings: Add a binding for Mediatek SCP

On Mon, Feb 25, 2019 at 12:15 AM Pi-Hsun Shih <pihsun@...omium.org> wrote:
>
> On Fri, Feb 22, 2019 at 10:43 PM Rob Herring <robh@...nel.org> wrote:
> >
> > On Thu, Feb 21, 2019 at 04:47:24PM +0800, Pi-Hsun Shih wrote:
> > > From: Erin Lo <erin.lo@...iatek.com>
> > >
> > > Add a DT binding documentation of SCP for the
> > > MT8183 SoC from Mediatek.
> > >
> > > Signed-off-by: Erin Lo <erin.lo@...iatek.com>
> > > ---
> > > Changes from v4:
> > >  - Add detail of more properties.
> > >  - Document the usage of mtk,rpmsg-name in subnode from the new design.
> > >
> > > Changes from v3:
> > >  - No change.
> > >
> > > Changes from v2:
> > >  - No change. I realized that for this patch series, there's no need to
> > >    add anything under the mt8183-scp node (neither the mt8183-rpmsg or
> > >    the cros-ec-rpmsg) for them to work, since mt8183-rpmsg is added
> > >    directly as a rproc_subdev by code, and cros-ec-rpmsg is dynamically
> > >    created by SCP name service.
> > >
> > > Changes from v1:
> > >  - No change.
> > > ---
> > >  .../bindings/remoteproc/mtk,scp.txt           | 37 +++++++++++++++++++
> > >  1 file changed, 37 insertions(+)
> > >  create mode 100644 Documentation/devicetree/bindings/remoteproc/mtk,scp.txt
> > >
> > > diff --git a/Documentation/devicetree/bindings/remoteproc/mtk,scp.txt b/Documentation/devicetree/bindings/remoteproc/mtk,scp.txt
> > > new file mode 100644
> > > index 00000000000000..8cf8b0e0d98a4c
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/remoteproc/mtk,scp.txt
> > > @@ -0,0 +1,37 @@
> > > +Mediatek SCP Bindings
> > > +----------------------------------------
> > > +
> > > +This binding provides support for ARM Cortex M4 Co-processor found on some
> > > +Mediatek SoCs.
> > > +
> > > +Required properties:
> > > +- compatible         Should be "mediatek,mt8183-scp"
> > > +- reg                        Should contain the address ranges for the two memory
> > > +                     regions, SRAM and CFG.
> > > +- reg-names          Contains the corresponding names for the two memory
> > > +                     regions. These should be named "sram" & "cfg".
> > > +- clocks             Clock for co-processor (See: ../clock/clock-bindings.txt)
> > > +- clock-names                Contains the corresponding name for the clock. This
> > > +                     should be named "main".
> > > +
> > > +Subnodes
> > > +--------
> > > +
> > > +When CONFIG_RPMSG_MTK_SCP is enabled, subnodes of the SCP represent rpmsg
> >
> > Bindings can't depend on kernel config options.
> >
>
> What's the recommendation here if the subnode only has effect when the
> config is enabled? Should I just skip the sentence "When ... is
> enabled"?

Sure.

>
> > > +devices. The names of the devices are not important. The properties of these
> > > +nodes are defined by the individual bindings for the rpmsg devices - but must
> > > +contain the following property:
> > > +
> > > +- mtk,rpmsg-name     Contains the name for the rpmsg device. Used to match
> > > +                     the subnode to rpmsg device announced by SCP.
> >
> > I don't think this belongs in DT, but without some examples I'm not
> > really sure.
> >
>
> This is similar to the qcom,smd-channels property in
> Documentation/devicetree/bindings/soc/qcom/qcom,smd.txt, a example DT
> for this:

QCom has lots of strange buses and communication channels. Probably
not the best place for inspiration.

> scp {
>         compatible = "mediatek,mt8183-scp";
>         ...
>         cros_ec {
>                 compatible = "google,cros-ec-rpmsg";
>                 mtk,rpmsg-name = "cros-ec-rpmsg";

Why do we need the same string twice? It's just the compatible string
minus the vendor prefix.

>
>                 cros_ec_codec {
>                         compatible = "google,cros-ec-codec";
>                         ...

What's this? I can't review bindings piece by piece.

>                 };
>         };
> };
>
> > > +
> > > +Example:
> > > +
> > > +     scp: scp@...00000 {
> > > +             compatible = "mediatek,mt8183-scp";
> > > +             reg = <0 0x10500000 0 0x80000>,
> > > +                   <0 0x105c0000 0 0x5000>;
> > > +             reg-names = "sram", "cfg";
> > > +             clocks = <&infracfg CLK_INFRA_SCPSYS>;
> > > +             clock-names = "main";
> > > +     };
> > > --
> > > 2.21.0.rc0.258.g878e2cd30e-goog
> > >