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

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Message-ID: <dca9e4c3e2ed61bf25a2d96a82a77e04@manjaro.org>
Date: Tue, 16 Jul 2024 22:11:02 +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

Hello Heiko,

On 2024-07-15 21:13, Heiko Stübner wrote:
> Am Montag, 15. Juli 2024, 20:01:35 CEST schrieb Dragan Simic:
>> 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.
> 
> you're talking about the driver ... we're in the hardware-binding here.
> Those are two completely different topics ;-) .
> 
> Devicetree is always about describing the hardware as best as possible,
> so you don't want too many "generics" there, because we're always 
> talking
> about specific ICs soldered to some board.
> 
> I also "violated" that in my v1 by grouping in the the Diodes parts, 
> which
> as Stephen pointed out are quite different afterall.

I'll make sure to go through the v1 discussion in detail ASAP.  After
that, I'll come back with some more thoughts.