linux-kernel - Re: [PATCH v3 6/7] dt-bindings: clock: meson: add A1 CPU clock controller bindings

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Date: Thu, 13 Jun 2024 12:03:30 +0300
From: Dmitry Rokosov <ddrokosov@...utedevices.com>
To: Jerome Brunet <jbrunet@...libre.com>
CC: <neil.armstrong@...aro.org>, <mturquette@...libre.com>,
	<sboyd@...nel.org>, <robh+dt@...nel.org>,
	<krzysztof.kozlowski+dt@...aro.org>, <khilman@...libre.com>,
	<martin.blumenstingl@...glemail.com>, <jian.hu@...ogic.com>,
	<kernel@...rdevices.ru>, <rockosov@...il.com>,
	<linux-amlogic@...ts.infradead.org>, <linux-clk@...r.kernel.org>,
	<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v3 6/7] dt-bindings: clock: meson: add A1 CPU clock
 controller bindings

On Mon, Jun 10, 2024 at 03:48:42PM +0300, Dmitry Rokosov wrote:
> On Mon, Jun 10, 2024 at 01:47:06PM +0200, Jerome Brunet wrote:
> > On Mon 10 Jun 2024 at 14:18, Dmitry Rokosov <ddrokosov@...utedevices.com> wrote:
> > 
> > > Hello Jerome,
> > >
> > > Thank you for the review!
> > >
> > > On Mon, Jun 10, 2024 at 12:04:09PM +0200, Jerome Brunet wrote:
> > >> On Wed 15 May 2024 at 21:47, Dmitry Rokosov <ddrokosov@...utedevices.com> wrote:
> > >> 
> > >> > Add the documentation and dt bindings for Amlogic A1 CPU clock
> > >> > controller.
> > >> >
> > >> > This controller consists of the general 'cpu_clk' and two main parents:
> > >> > 'cpu fixed clock' and 'syspll'. The 'cpu fixed clock' is an internal
> > >> > fixed clock, while the 'syspll' serves as an external input from the A1
> > >> > PLL clock controller.
> > >> >
> > >> > Signed-off-by: Dmitry Rokosov <ddrokosov@...utedevices.com>
> > >> > Reviewed-by: Rob Herring <robh@...nel.org>
> > >> > ---
> > >> >  .../bindings/clock/amlogic,a1-cpu-clkc.yaml   | 64 +++++++++++++++++++
> > >> >  .../dt-bindings/clock/amlogic,a1-cpu-clkc.h   | 19 ++++++
> > >> >  2 files changed, 83 insertions(+)
> > >> >  create mode 100644 Documentation/devicetree/bindings/clock/amlogic,a1-cpu-clkc.yaml
> > >> >  create mode 100644 include/dt-bindings/clock/amlogic,a1-cpu-clkc.h
> > >> >
> > >> > diff --git a/Documentation/devicetree/bindings/clock/amlogic,a1-cpu-clkc.yaml b/Documentation/devicetree/bindings/clock/amlogic,a1-cpu-clkc.yaml
> > >> > new file mode 100644
> > >> > index 000000000000..f4958b315ed4
> > >> > --- /dev/null
> > >> > +++ b/Documentation/devicetree/bindings/clock/amlogic,a1-cpu-clkc.yaml
> > >> > @@ -0,0 +1,64 @@
> > >> > +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> > >> > +%YAML 1.2
> > >> > +---
> > >> > +$id: http://devicetree.org/schemas/clock/amlogic,a1-cpu-clkc.yaml#
> > >> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > >> > +
> > >> > +title: Amlogic A1 CPU Clock Control Unit
> > >> > +
> > >> > +maintainers:
> > >> > +  - Neil Armstrong <neil.armstrong@...aro.org>
> > >> > +  - Jerome Brunet <jbrunet@...libre.com>
> > >> > +  - Dmitry Rokosov <ddrokosov@...utedevices.com>
> > >> > +
> > >> > +properties:
> > >> > +  compatible:
> > >> > +    const: amlogic,a1-cpu-clkc
> > >> > +
> > >> > +  '#clock-cells':
> > >> > +    const: 1
> > >> > +
> > >> > +  reg:
> > >> > +    maxItems: 1
> > >> > +
> > >> > +  clocks:
> > >> > +    items:
> > >> > +      - description: input fixed pll div2
> > >> > +      - description: input fixed pll div3
> > >> > +      - description: input sys pll
> > >> > +      - description: input oscillator (usually at 24MHz)
> > >> 
> > >> According to the documentation, fdiv5 is also an input of the CPU clock
> > >> tree.
> > >> 
> > >> That is typically the kind of things we'd prefer to get right from the
> > >> beginning to avoid modifying the bindings later.
> > >> 
> > >
> > > Could you please share which documentation you are referencing? I have
> > > the A113L documentation, and there is no mention of the CPU clock IP.
> > 
> > You should get in touch with Amlogic.
> > 
> 
> Okay, I will double check with Amlogic and back with accurate
> information.
> 

According to a statement from an Amlogic FAE, there is an error in the
datasheet's CPU clock controller figure. The FAE clarified the
following:

"""
The d5/d7 clock source inside the A1 chip is not supplied to CPU_CLK and
is instead used by other peripherals. Therefore, you can connect a fixed
frequency divider (div5/div7) to peripherals in A1. The CPU control only
supports fclk_div2/div3.
"""

[...]

-- 
Thank you,
Dmitry