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

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Date:   Tue, 18 Dec 2018 15:35:03 +0100
From:   Niklas Cassel <niklas.cassel@...aro.org>
To:     Stephen Boyd <sboyd@...nel.org>
Cc:     andy.gross@...aro.org, david.brown@...aro.org,
        jassisinghbrar@...il.com, jorge.ramirez-ortiz@...aro.org,
        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

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.


Kind regards,
Niklas