linux-kernel - Re: [PATCH v2 1/3] dt-bindings: clocks: add binding for voltage-controlled-oscillators

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Message-ID: <3f0c241d39c5fedb674d7f9808d0be8f@manjaro.org>
Date: Mon, 15 Jul 2024 20:01:35 +0200
From: Dragan Simic <dsimic@...jaro.org>
To: Heiko Stübner <heiko@...ech.de>
Cc: 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

On 2024-07-15 19:46, Heiko Stübner wrote:
> Am Montag, 15. Juli 2024, 17:15:45 CEST schrieb Dragan Simic:
>> On 2024-07-15 13:02, 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
>> 
>> Frankly, I find the "voltage-oscillator" and "voltage controlled
>> oscillator" names awkward.  In general, "clock" is used throughout
>> the entire kernel, when it comes to naming files and defining
>> "compatible" strings.  Thus, I'd suggest that "clock" is used here
>> instead of "oscillator", because it's consistent and shorter.
>> 
>> How about using "gated-clock" for the "compatible" string, and
>> "Simple gated clock generator" instead of "voltage controlled
>> oscillator"?  Besides sounding awkward, "voltage controlled
>> oscillator" may suggest that the clock generator can be adjusted
>> or programmed somehow by applying the voltage, while it can only
>> be enabled or disabled that way, which is by definition clock
>> gating.  Thus, "gated-clock" and "Simple gated clock generator"
>> would fit very well.
> 
> The naming came from Stephen - one of the clock maintainers ;-)
> See discussion in v1. Who also described these things as
> "voltage-controlled-oscillators".
> 
> And from that discussion I also got the impression we should aim for
> more specific naming - especially when talking about dt-bindings, for 
> this
> "usage in the Linux kernel" actually isn't a suitable metric and
> "gated-clock" is probably way too generic I think.

I see, thanks for the clarification.  Though, the generic nature of
"gated-clock" as the name may actually make this driver a bit more
future-proof, by allowing some other features to be added to it at
some point in the future, avoiding that way the need for yet another
kernel driver.

> Though I'm not attached to any specific naming, so we'll simply
> wait for the clock- and dt-maintainers to weigh in ;-)