linux-kernel - Re: [PATCH 1/6] dt-bindings: clocks: add binding for generic clock-generators

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Message-ID: <21244242.0c2gjJ1VT2@diego>
Date: Wed, 10 Jul 2024 09:45:17 +0200
From: Heiko Stübner <heiko@...ech.de>
To: mturquette@...libre.com, sboyd@...nel.org,
 Alexander Stein <alexander.stein@...tq-group.com>
Cc: robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
 quentin.schulz@...rry.de, 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 1/6] dt-bindings: clocks: add binding for generic clock-generators

Hi,

Am Mittwoch, 10. Juli 2024, 09:02:34 CEST schrieb Alexander Stein:
> Am Dienstag, 9. Juli 2024, 14:31:16 CEST schrieb Heiko Stuebner:
> > In contrast to fixed clocks that are described as ungateable, boards
> > sometimes use additional clock generators for things like PCIe reference
> > clocks, that need actual supplies to get enabled and enable-gpios to be
> > toggled for them to work.
> 
> Fixed clocks are intended to be ungateable? Where does this come from?

"DOC: basic fixed-rate clock that cannot gate"
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/clk/clk-fixed-rate.c#n18


> > This adds a binding for such clock generators that are not configurable
> > themself, but need to handle supplies for them to work.
> > 
> > While in a lot of cases the type of the IC used is described in board
> > schematics, in some cases just a generic type description like
> > "100MHz, 3.3V" might also be used. The binding therefore allows both
> > cases. Specifying the type is of course preferred.
> > 
> > The clock-frequency is set in devicetree, because while some clock
> > generators have pins to decide between multipls output rates, those
> > are generally set statically on the board-layout-level.
> > 
> > Signed-off-by: Heiko Stuebner <heiko@...ech.de>
> > ---
> >  .../bindings/clock/clock-generator.yaml       | 62 +++++++++++++++++++
> >  1 file changed, 62 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/clock/clock-generator.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/clock/clock-generator.yaml b/Documentation/devicetree/bindings/clock/clock-generator.yaml
> > new file mode 100644
> > index 0000000000000..f44e61e414e89
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/clock/clock-generator.yaml
> > @@ -0,0 +1,62 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/clock/clock-generator.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Simple clock generators
> > +
> > +maintainers:
> > +  - Heiko Stuebner <heiko@...ech.de>
> > +
> > +properties:
> > +  $nodename:
> > +    anyOf:
> > +      - description:
> > +          Preferred name is 'clock-<freq>' with <freq> being the output
> > +          frequency as defined in the 'clock-frequency' property.
> > +        pattern: "^clock-([0-9]+|[a-z0-9-]+)$"
> > +      - description: Any name allowed
> > +        deprecated: true
> > +
> > +  compatible:
> > +    oneOf:
> > +      - const: clock-generator
> > +      - items:
> > +          - enum:
> > +              - diodes,pi6c557-03b
> > +              - diodes,pi6c557-05b
> > +          - const: clock-generator
> > +
> > +  "#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 clock generator.
> > +    maxItems: 1
> > +
> > +  vdd-supply:
> > +    description: handle of the regulator that provides the supply voltage
> 
> So essentially only enable-gpios and vdd-supply is added in comparison to
> fixed-clock. Does it make sense to add that to the fixed-clocks instead?
> Similar to fixed-regulator.

I wasn't that sure which way to go in the first place.
The deciding point was reading that line about the fixed clock not
being gateable, so I opted to not touch the fixed-clock.

But you're definitly right, this _could_ live inside the fixed-clock
as well, if we decide to get rid of the not-gateable thing above.


Heiko