linux-kernel - Re: [RESEND/PATCH v6 3/3] clk: qcom: Add A53 clock driver

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Message-ID: <20161102225520.GW16026@codeaurora.org>
Date:   Wed, 2 Nov 2016 15:55:20 -0700
From:   Stephen Boyd <sboyd@...eaurora.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Georgi Djakov <georgi.djakov@...aro.org>, mturquette@...libre.com,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>
Subject: Re: [RESEND/PATCH v6 3/3] clk: qcom: Add A53 clock driver

On 11/02, Bjorn Andersson wrote:
> On Thu 27 Oct 18:54 PDT 2016, Stephen Boyd wrote:
> 
> > On 10/19, Georgi Djakov wrote:
> > > Add a driver for the A53 Clock Controller. It is a hardware block that
> > > implements a combined mux and half integer divider functionality. It can
> > > choose between a fixed-rate clock or the dedicated A53 PLL. The source
> > > and the divider can be set both at the same time.
> > > 
> > > This is required for enabling CPU frequency scaling on platforms like
> > > MSM8916.
> > > 
> > 
> > Please Cc DT reviewers.
> > 
> > > Signed-off-by: Georgi Djakov <georgi.djakov@...aro.org>
> > > ---
> > >  .../devicetree/bindings/clock/qcom,a53cc.txt       |  22 +++
> > >  drivers/clk/qcom/Kconfig                           |   8 ++
> > >  drivers/clk/qcom/Makefile                          |   1 +
> > >  drivers/clk/qcom/a53cc.c                           | 155 +++++++++++++++++++++
> > >  4 files changed, 186 insertions(+)
> > >  create mode 100644 Documentation/devicetree/bindings/clock/qcom,a53cc.txt
> > >  create mode 100644 drivers/clk/qcom/a53cc.c
> > > 
> > > diff --git a/Documentation/devicetree/bindings/clock/qcom,a53cc.txt b/Documentation/devicetree/bindings/clock/qcom,a53cc.txt
> > > new file mode 100644
> > > index 000000000000..a025f062f177
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/clock/qcom,a53cc.txt
> > > @@ -0,0 +1,22 @@
> > > +Qualcomm A53 CPU Clock Controller Binding
> > > +------------------------------------------------
> > > +The A53 CPU Clock Controller is hardware, which provides a combined
> > > +mux and divider functionality for the CPU clocks. It can choose between
> > > +a fixed rate clock and the dedicated A53 PLL.
> > > +
> > > +Required properties :
> > > +- compatible : shall contain:
> > > +
> > > +			"qcom,a53cc"
> > > +
> > > +- reg : shall contain base register location and length
> > > +	of the APCS region
> > > +- #clock-cells : shall contain 1
> > > +
> > > +Example:
> > > +
> > > +	apcs: syscon@...1000 {
> > > +		compatible = "qcom,a53cc", "syscon";
> > 
> > Why is it a syscon? Is that part used?
> > 
> 
> I use the register at offset 8 for interrupting the other subsystems, so
> this must be available as something I can poke.
> 
> Which makes me think that this should be described as a "simple-mfd" and
> "syscon" with the a53cc node as a child - grabbing the regmap of the
> syscon parent, rather then ioremapping the same region again.
> 

That's sort of a question for DT reviewers. The register space
certainly seems like a free for all with a tilt toward power
management of the CPU, similar to how this was done on Krait
based designs.

I wonder why we didn't make up some provider/consumer binding for
the "kicking" feature used by SMD/RPM code. Then this could be a
clock provider and a "kick" provider (haha #kick-cells) and the
usage of syscon/regmap wouldn't be mandatory.

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