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

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Message-ID: <2186398.KiezcSG77Q@diego>
Date: Mon, 15 Jul 2024 21:13:45 +0200
From: Heiko Stübner <heiko@...ech.de>
To: Dragan Simic <dsimic@...jaro.org>
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

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.


Heiko