Message-ID: <30e4a6cb0ad489fa30efbfef2d6005d7@manjaro.org>
Date: Tue, 16 Jul 2024 19:54:07 +0200
From: Dragan Simic <dsimic@...jaro.org>
To: Conor Dooley <conor@...nel.org>
Cc: Heiko Stuebner <heiko@...ech.de>, mturquette@...libre.com,
 sboyd@...nel.org, robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
 linux-clk@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH v2 1/3] dt-bindings: clocks: add binding for
 voltage-controlled-oscillators

Hello Conor,

On 2024-07-16 18:15, Conor Dooley wrote:
> On Mon, Jul 15, 2024 at 01:02:49PM +0200, Heiko Stuebner wrote:
>> In contrast to fixed clocks that are described as ungateable, boards
>> sometimes use additional oscillators for things like PCIe reference
>> clocks, that need actual supplies to get enabled and enable-gpios to 
>> be
>> toggled for them to work.
>> 
>> This adds a binding for such oscillators that are not configurable
>> themself, but need to handle supplies for them to work.
>> 
>> In schematics they often can be seen as
>> 
>>          ----------------
>> Enable - | 100MHz,3.3V, | - VDD
>>          |    3225      |
>>    GND - |              | - OUT
>>          ----------------
>> 
>> or similar. The enable pin might be separate but can also just be tied
>> to the vdd supply, hence it is optional in the binding.
>> 
>> Signed-off-by: Heiko Stuebner <heiko@...ech.de>
>> ---
>>  .../bindings/clock/voltage-oscillator.yaml    | 49 
>> +++++++++++++++++++
>>  1 file changed, 49 insertions(+)
>>  create mode 100644 
>> Documentation/devicetree/bindings/clock/voltage-oscillator.yaml
>> 
>> diff --git 
>> a/Documentation/devicetree/bindings/clock/voltage-oscillator.yaml 
>> b/Documentation/devicetree/bindings/clock/voltage-oscillator.yaml
>> new file mode 100644
>> index 0000000000000..8bff6b0fd582e
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/clock/voltage-oscillator.yaml
>> @@ -0,0 +1,49 @@
>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/clock/voltage-oscillator.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: Voltage controlled oscillator
> 
> Voltage controlled oscillator? Really? That sounds far too similar to a
> VCO to me, and the input voltage here (according to the description at
> least) does not affect the frequency of oscillation.

Yup, "voltage controlled oscillator" really isn't the right choice for
the name, as I wrote about already. [1]

[1] 
https://lore.kernel.org/linux-rockchip/ec84dc37e2c421ee6d31294e08392d57@manjaro.org/

> Why the dedicated binding, rather than adding a supply and enable-gpio
> to the existing "fixed-clock" binding? I suspect that a large portion 
> of
> "fixed-clock"s actually require a supply that is (effectively)
> always-on.
> 
>> +
>> +maintainers:
>> +  - Heiko Stuebner <heiko@...ech.de>
>> +
>> +properties:
>> +  compatible:
>> +    const: voltage-oscillator
>> +
>> +  "#clock-cells":
>> +    const: 0
>> +
>> +  clock-frequency: true
>> +
>> +  clock-output-names:
>> +    maxItems: 1
>> +
>> +  enable-gpios:
>> +    description:
>> +      Contains a single GPIO specifier for the GPIO that enables and 
>> disables
>> +      the oscillator.
>> +    maxItems: 1
>> +
>> +  vdd-supply:
>> +    description: handle of the regulator that provides the supply 
>> voltage
>> +
>> +required:
>> +  - compatible
>> +  - "#clock-cells"
>> +  - clock-frequency
>> +  - vdd-supply
>> +
>> +additionalProperties: false
>> +
>> +examples:
>> +  - |
>> +    voltage-oscillator {
>> +      compatible = "voltage-oscillator";
>> +      #clock-cells = <0>;
>> +      clock-frequency = <1000000000>;
>> +      vdd-supply = <&reg_vdd>;
>> +    };
>> +...
>> --
>> 2.39.2
>> 
> 
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