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

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Message-ID: <20161114203426.GN5177@codeaurora.org>
Date:   Mon, 14 Nov 2016 14:21:22 -0800
From:   Stephen Boyd <sboyd@...eaurora.org>
To:     Georgi Djakov <georgi.djakov@...aro.org>
Cc:     Bjorn Andersson <bjorn.andersson@...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 11/11, Georgi Djakov wrote:
> On 11/03/2016 08:28 PM, Bjorn Andersson wrote:
> >On Wed 02 Nov 15:55 PDT 2016, Stephen Boyd wrote:
> >
> >>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.
> >>
> >
> >Right. But this kind of mashup blocks was the reason why simple-mfd was
> >put in place.
> >
> 
> Ok, thanks for the comments. Then i will make it look like this:
> 
> 	apcs: syscon@...1000 {
> 		compatible = "syscon", "simple-mfd";
> 		reg = <0x0b011000 0x1000>;
> 
> 		a53mux: clock {
> 			compatible = "qcom,msm8916-a53cc";
> 			#clock-cells = <1>;
> 		};
> 	};
> 
> Thanks,
> Georgi
> 
> >>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.
> >>
> >
> >I did consider doing that, but had enough dependencies to put in place
> >as it was.
> >
> >I'm in favour of us inventing a kicker API and it's found outside out
> >use cases as well (e.g. virtio/rpmsg).
> >

I'd rather we did this kicker API as well. That way we don't need
to make a syscon and a simple-mfd to get software to work
properly. Don't other silicon vendors need a kicker API as well?
How are they kicking remote processors in other places? GPIOs?

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