linux-kernel - Re: [PATCH 1/5] Documentation: dt: binding: fsl: Add 'fsl,ippdexpcr1-alt-addr' property

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Message-ID: <CAL_Jsq+uzkr7CcvwQTe5vhpMPtdqL9v4EeqH5yZjMoT=JrDtDQ@mail.gmail.com>
Date:   Mon, 28 Sep 2020 08:56:51 -0500
From:   Rob Herring <robh@...nel.org>
To:     Ran Wang <ran.wang_1@....com>
Cc:     Leo Li <leoyang.li@....com>, Shawn Guo <shawnguo@...nel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Biwen Li <biwen.li@....com>
Subject: Re: [PATCH 1/5] Documentation: dt: binding: fsl: Add
 'fsl,ippdexpcr1-alt-addr' property

On Wed, Sep 23, 2020 at 1:44 AM Ran Wang <ran.wang_1@....com> wrote:
>
> Hi Rob,
>
> On Wednesday, September 23, 2020 10:33 AM, Rob Herring wrote:
> >
> > On Wed, Sep 16, 2020 at 04:18:27PM +0800, Ran Wang wrote:
> > > From: Biwen Li <biwen.li@....com>
> > >
> > > The 'fsl,ippdexpcr1-alt-addr' property is used to handle an errata
> > > A-008646 on LS1021A
> > >
> > > Signed-off-by: Biwen Li <biwen.li@....com>
> > > Signed-off-by: Ran Wang <ran.wang_1@....com>
> > > ---
> > >  Documentation/devicetree/bindings/soc/fsl/rcpm.txt | 19
> > > +++++++++++++++++++
> > >  1 file changed, 19 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/soc/fsl/rcpm.txt
> > > b/Documentation/devicetree/bindings/soc/fsl/rcpm.txt
> > > index 5a33619..1be58a3 100644
> > > --- a/Documentation/devicetree/bindings/soc/fsl/rcpm.txt
> > > +++ b/Documentation/devicetree/bindings/soc/fsl/rcpm.txt
> > > @@ -34,6 +34,11 @@ Chassis Version          Example Chips
> > >  Optional properties:
> > >   - little-endian : RCPM register block is Little Endian. Without it RCPM
> > >     will be Big Endian (default case).
> > > + - fsl,ippdexpcr1-alt-addr : The property is related to a hardware issue
> > > +   on SoC LS1021A and only needed on SoC LS1021A.
> > > +   Must include 2 entries:
> > > +   The first entry must be a link to the SCFG device node.
> > > +   The 2nd entry must be offset of register IPPDEXPCR1 in SCFG.
> >
> > You don't need a DT change for this. You can find SCFG node by its compatible
> > string and then the offset should be known given this issue is only on 1 SoC.
>
> Did you mean that RCPM driver just to access IPPDEXPCR1 shadowed register in SCFG
> directly without fetching it's offset info. from DT?

Yes. There's only 1 possible value of the offset because there's only
one SoC, so the driver can hardcode the offset. And I assume there's
only one SCFG node, so you can find it by its compatible string
(of_find_compatible_node).

Rob