linux-kernel - Re: [PATCH 05/13] clk: qcom: apcs-msm8916: get parent clock names from DT

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Message-ID: <154603613437.179992.1170701312259011363@swboyd.mtv.corp.google.com>
Date:   Fri, 28 Dec 2018 14:28:54 -0800
From:   Stephen Boyd <sboyd@...nel.org>
To:     Jorge Ramirez <jorge.ramirez-ortiz@...aro.org>,
        Niklas Cassel <niklas.cassel@...aro.org>
Cc:     andy.gross@...aro.org, david.brown@...aro.org,
        jassisinghbrar@...il.com, mark.rutland@....com,
        mturquette@...libre.com, robh+dt@...nel.org, will.deacon@....com,
        bjorn.andersson@...aro.org, vkoul@...nel.org, sibis@...eaurora.org,
        georgi.djakov@...aro.org, arnd@...db.de,
        horms+renesas@...ge.net.au, heiko@...ech.de,
        enric.balletbo@...labora.com, jagan@...rulasolutions.com,
        olof@...om.net, amit.kucheria@...aro.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org
Subject: Re: [PATCH 05/13] clk: qcom: apcs-msm8916: get parent clock names from DT

Quoting Jorge Ramirez (2018-12-26 01:20:07)
> On 12/18/18 15:35, Niklas Cassel wrote:
> > On Mon, Dec 17, 2018 at 03:37:43PM -0800, Stephen Boyd wrote:
> >> Quoting Jorge Ramirez-Ortiz (2018-12-17 01:46:22)
> >>> Allow accessing the parent clock names required for the driver
> >>> operation by using the device tree node.
> >>>
> >>> This permits extending the driver to other platforms without having to
> >>> modify its source code.
> >>>
> >>> For backwards compatibility leave previous values as default.
> >>
> >> Why do we need to maintain backwards compatibility? Isn't is required
> >> that the nodes have clocks properties?
> >>
> > 
> > Hello Stephen,
> > 
> > 
> > This is the existing DT nodes for msm8916:
> > 
> >                 a53pll: clock@...6000 {
> >                          compatible = "qcom,msm8916-a53pll";
> >                          reg = <0xb016000 0x40>;
> >                          #clock-cells = <0>;
> >                  };
> > 
> >                  apcs: mailbox@...1000 {
> >                          compatible = "qcom,msm8916-apcs-kpss-global", "syscon";
> >                          reg = <0xb011000 0x1000>;
> >                          #mbox-cells = <1>;
> >                          clocks = <&a53pll>;
> >                          #clock-cells = <0>;
> >                  };
> > 
> > 
> > This is the (suggested) DT nodes for qcs404:
> > 
> >                  apcs_hfpll: clock-controller@...16000 {
> >                          compatible = "qcom,hfpll";
> >                          reg = <0x0b016000 0x30>;
> >                          #clock-cells = <0>;
> >                          clock-output-names = "apcs_hfpll";
> >                          clocks = <&xo_board>;
> >                          clock-names = "xo";
> >                  };
> > 
> >                  apcs_glb: mailbox@...1000 {
> >                          compatible = "qcom,qcs404-apcs-apps-global", "syscon";
> >                          reg = <0x0b011000 0x1000>;
> >                          #mbox-cells = <1>;
> >                          clocks = <&gcc GCC_GPLL0_AO_OUT_MAIN>, <&apcs_hfpll>;
> >                          clock-names = "aux", "pll";
> >                          #clock-cells = <0>;
> >                  };
> > 
> > qcs404 specifies two clocks, with an accompanied clock-name for each clock.
> > 
> > msm8916 specifies a single clock, without an accompanied clock-name.
> > 
> > It is possible to append clock-names = "pll" for the existing clock,
> > as well as to define the aux clock in the apcs node in the msm8916 DT:
> > clocks = <&gcc GPLL0_VOTE>;
> > clock-names = "aux";
> > 
> > However, since the DT is treated as an ABI, the existing DT for msm8916 must
> > still work, so I don't think that it is possible to ignore having backwards
> > compability in the apcs clock driver.
> 
> 
> so where are we with this?
> 
> do we remove backwards compatibility (see below] for v2 or is the DT 
> really an ABI and therefore the patch under review is good as is?
> 

Breaking compatibility is up to the platform maintainers. If anything, I
would make the DTS and driver changes in parallel and then remove the
driver's backwards compatibility logic later on.