linux-kernel - Re: [PATCH v2 03/18] dt-bindings: clk: Add documentation of grx500 clock controller

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Date:   Wed, 8 Aug 2018 08:54:12 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     yixin zhu <yixin.zhu@...ux.intel.com>
Cc:     Songjun Wu <songjun.wu@...ux.intel.com>, hua.ma@...ux.intel.com,
        chuanhua.lei@...ux.intel.com, qi-ming.wu@...el.com,
        Linux-MIPS <linux-mips@...ux-mips.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        devicetree@...r.kernel.org,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v2 03/18] dt-bindings: clk: Add documentation of grx500
 clock controller

On Tue, Aug 7, 2018 at 9:08 PM yixin zhu <yixin.zhu@...ux.intel.com> wrote:
>
>
>
> On 8/6/2018 11:18 PM, Rob Herring wrote:
> > On Thu, Aug 2, 2018 at 9:03 PM Songjun Wu <songjun.wu@...ux.intel.com> wrote:
> >> From: Yixin Zhu <yixin.zhu@...ux.intel.com>
> >>
> >> This patch adds binding documentation for grx500 clock controller.
> >>
> >> Signed-off-by: YiXin Zhu <yixin.zhu@...ux.intel.com>
> >> Signed-off-by: Songjun Wu <songjun.wu@...ux.intel.com>
> >> ---
> >>
> >> Changes in v2:
> >> - Rewrite clock driver's dt-binding document according to Rob Herring's
> >>    comments.
> >> - Simplify device tree docoment, remove some clock description.
> >>
> >>   .../devicetree/bindings/clock/intel,grx500-clk.txt | 39 ++++++++++++++++++++++
> > Please match the compatible string: intel,grx500-cgu.txt
> Will update to use same name.
>
> >
> >>   1 file changed, 39 insertions(+)
> >>   create mode 100644 Documentation/devicetree/bindings/clock/intel,grx500-clk.txt
> >>
> >> diff --git a/Documentation/devicetree/bindings/clock/intel,grx500-clk.txt b/Documentation/devicetree/bindings/clock/intel,grx500-clk.txt
> >> new file mode 100644
> >> index 000000000000..e54e1dad9196
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/clock/intel,grx500-clk.txt
> >> @@ -0,0 +1,39 @@
> >> +Device Tree Clock bindings for grx500 PLL controller.
> >> +
> >> +This binding uses the common clock binding:
> >> +       Documentation/devicetree/bindings/clock/clock-bindings.txt
> >> +
> >> +The grx500 clock controller supplies clock to various controllers within the
> >> +SoC.
> >> +
> >> +Required properties for clock node
> >> +- compatible: Should be "intel,grx500-cgu".
> >> +- reg: physical base address of the controller and length of memory range.
> >> +- #clock-cells: should be 1.
> >> +
> >> +Optional Propteries:
> >> +- intel,osc-frequency: frequency of the osc clock.
> >> +if missing, driver will use clock rate defined in the driver.
> > This should use a fixed-clock node instead.
> Yes, This is a fixed clock node registered in driver code.
> The frequency of the fixed clock is designed to be overwritten by device
> tree in case some one verify
> clock driver in the emulation platform or in some cases frequency other
> than driver defined one is preferred.

Emulation platforms often need several hacks that shouldn't be upstream...

> These kinds of cases are very rare. But I feel it would be better to
> have a way to use customized frequency.
> The frequency defined in device tree will overwritten driver defined
> frequency before registering fixed-clock node.

I don't think you understand what I meant. Add a DT node with
"fixed-clock" compatible and have this node refer to it with "clocks"
property. The frequency is still in DT, but uses the clock binding.

Rob