linux-kernel - Re: [v3,3/3] Documentation: dt: binding: fsl: Add 'fsl,ippdexpcr-alt-addr' property

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Message-ID: <20190927182844.GA5203@bogus>
Date:   Fri, 27 Sep 2019 13:28:44 -0500
From:   Rob Herring <robh@...nel.org>
To:     Leo Li <leoyang.li@....com>
Cc:     Biwen Li <biwen.li@....com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        Ran Wang <ran.wang_1@....com>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [v3,3/3] Documentation: dt: binding: fsl: Add
 'fsl,ippdexpcr-alt-addr' property

On Wed, Sep 25, 2019 at 03:34:47AM +0000, Leo Li wrote:
> 
> 
> > -----Original Message-----
> > From: Biwen Li
> > Sent: Tuesday, September 24, 2019 10:30 PM
> > To: Leo Li <leoyang.li@....com>; shawnguo@...nel.org;
> > robh+dt@...nel.org; mark.rutland@....com; Ran Wang
> > <ran.wang_1@....com>
> > Cc: linuxppc-dev@...ts.ozlabs.org; linux-arm-kernel@...ts.infradead.org;
> > linux-kernel@...r.kernel.org; devicetree@...r.kernel.org
> > Subject: RE: [v3,3/3] Documentation: dt: binding: fsl: Add 'fsl,ippdexpcr-alt-
> > addr' property
> > 
> > > > > >
> > > > > > The 'fsl,ippdexpcr-alt-addr' property is used to handle an
> > > > > > errata
> > > > > > A-008646 on LS1021A
> > > > > >
> > > > > > Signed-off-by: Biwen Li <biwen.li@....com>
> > > > > > ---
> > > > > > Change in v3:
> > > > > > 	- rename property name
> > > > > > 	  fsl,rcpm-scfg -> fsl,ippdexpcr-alt-addr
> > > > > >
> > > > > > Change in v2:
> > > > > > 	- update desc of the property 'fsl,rcpm-scfg'
> > > > > >
> > > > > >  Documentation/devicetree/bindings/soc/fsl/rcpm.txt | 14
> > > > > > ++++++++++++++
> > > > > >  1 file changed, 14 insertions(+)
> > > > > >
> > > > > > diff --git a/Documentation/devicetree/bindings/soc/fsl/rcpm.txt
> > > > > > b/Documentation/devicetree/bindings/soc/fsl/rcpm.txt
> > > > > > index 5a33619d881d..157dcf6da17c 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,ippdexpcr-alt-addr : Must add the property for SoC
> > > > > > + LS1021A,
> > > > >
> > > > > You probably should mention this is related to a hardware issue on
> > > > > LS1021a and only needed on LS1021a.
> > > > Okay, got it, thanks, I will add this in v4.
> > > > >
> > > > > > +   Must include n + 1 entries (n = #fsl,rcpm-wakeup-cells, such as:
> > > > > > +   #fsl,rcpm-wakeup-cells equal to 2, then must include 2 + 1 entries).
> > > > >
> > > > > #fsl,rcpm-wakeup-cells is the number of IPPDEXPCR registers on an SoC.
> > > > > However you are defining an offset to scfg registers here.  Why
> > > > > these two are related?  The length here should actually be related
> > > > > to the #address-cells of the soc/.  But since this is only needed
> > > > > for LS1021, you can
> > > > just make it 3.
> > > > I need set the value of IPPDEXPCR resgiters from ftm_alarm0 device
> > > > node(fsl,rcpm-wakeup = <&rcpm 0x0 0x20000000>;
> > > > 0x0 is a value for IPPDEXPCR0, 0x20000000 is a value for IPPDEXPCR1).
> > > > But because of the hardware issue on LS1021A, I need store the value
> > > > of IPPDEXPCR registers to an alt address. So I defining an offset to
> > > > scfg registers, then RCPM driver get an abosolute address from
> > > > offset, RCPM driver write the value of IPPDEXPCR registers to these
> > > > abosolute addresses(backup the value of IPPDEXPCR registers).
> > >
> > > I understand what you are trying to do.  The problem is that the new
> > > fsl,ippdexpcr-alt-addr property contains a phandle and an offset.  The
> > > size of it shouldn't be related to #fsl,rcpm-wakeup-cells.
> > You maybe like this: fsl,ippdexpcr-alt-addr = <&scfg 0x51c>;/*
> > SCFG_SPARECR8 */
> 
> No.  The #address-cell for the soc/ is 2, so the offset to scfg 
> should be 0x0 0x51c.  The total size should be 3, but it shouldn't be 
> coming from #fsl,rcpm-wakeup-cells like you mentioned in the binding.

Um, no. #address-cells applies to reg and ranges, not some vendor 
specific property. You can just define how many cells you need if that's 
fixed. 

However, I suggested doing this another way in the next version of this.

Rob