Re: [PATCH v3 1/2] dt-bindings: Add GPIO-locked fixed clock

[Conor Dooley <conor@kernel.org>]

[-- Attachment #1: Type: text/plain, Size: 4276 bytes --]

On Mon, Jun 15, 2026 at 06:01:34PM -0400, Brian Masney wrote:
> Hi Vyacheslav,
> 
> On Wed, Jun 03, 2026 at 11:16:42AM +0000, Vyacheslav Yurkov via B4 Relay wrote:
> > From: Vyacheslav Yurkov <V.Yurkov.EXT@bruker.com>
> > 
> > Some hardware designs provide fixed-frequency clocks generated outside
> > software control, such as by FPGA-resident PLLs. While the clock rate is
> > fixed, a separate GPIO signal indicates whether the clock source is
> > locked and producing a valid output.
> > 
> > Describe a GPIO-locked fixed clock provider that exposes a fixed-rate
> > clock whose availability depends on one or more GPIO lock-status
> > signals.
> > 
> > Signed-off-by: Vyacheslav Yurkov <uvv.mail@gmail.com>
> > Signed-off-by: Vyacheslav Yurkov <V.Yurkov.EXT@bruker.com>
> > ---
> >  .../bindings/clock/gpio-locked-fixed-clock.yaml    | 70 ++++++++++++++++++++++
> >  1 file changed, 70 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/clock/gpio-locked-fixed-clock.yaml b/Documentation/devicetree/bindings/clock/gpio-locked-fixed-clock.yaml
> > new file mode 100644
> > index 000000000000..9106b800b673
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/clock/gpio-locked-fixed-clock.yaml
> > @@ -0,0 +1,70 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/clock/gpio-locked-fixed-clock.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: GPIO Locked Fixed Clock
> > +
> > +maintainers:
> > +  - Vyacheslav Yurkov <V.Yurkov.EXT@bruker.com>
> > +
> > +description: |
> > +  Provides a clock output whose availability depends on a set of
> > +  prerequisite conditions. These conditions include the presence of
> > +  one or more parent clocks and the asserted state of one or more
> > +  GPIO lock indicators. An example of such clocks is FPGA clock that
> > +  are outside CPU control, with the lock status exposed through GPIO
> > +  signal.
> > +
> > +  The output clock is considered available only when all configured
> > +  prerequisites are satisfied.
> 
> I'm stepping outside my usual review of just the clk drivers. Krzysztof
> in v1 and v2 asked for more detailed hardware explanation. This feels to
> me like this is a policy that says to not use these clocks until the
> GPIO says they are ready. My gut feeling is that details like this
> should live in a clk driver instead of a dt-binding.
> 
> Alternatively, if this is generic enough, then could
> Documentation/devicetree/bindings/clock/gated-fixed-clock.yaml be
> extended?

FWIW this came up in an earlier revision:
https://lore.kernel.org/all/20260407-fling-scouring-dbe2141cc79b@spud/

IMO it's an inverted gpio-gate-clock, where the gpio is an input rather
than an output. I suppose you could extend gpio-gate-clock with it and
have mutually exclusive enable-gpios and status-gpios?

> 
> Brian
> 
> 
> > +
> > +properties:
> > +  compatible:
> > +    const: gpio-locked-fixed-clock
> > +
> > +  "#clock-cells":
> > +    const: 0
> > +
> > +  clocks:
> > +    description: Input clocks whose validity is monitored by this provider.
> > +
> > +  clock-output-names:
> > +    description: Names of the clock provided by this controller.
> > +    maxItems: 1
> > +
> > +  locked-gpios:
> > +    description: |
> > +      GPIOs to check the lock state.
> > +    minItems: 1
> > +    maxItems: 32
> > +
> > +required:
> > +  - compatible
> > +  - "#clock-cells"
> > +
> > +anyOf:
> > +  - required:
> > +      - clocks
> > +  - required:
> > +      - locked-gpios
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    #include <dt-bindings/gpio/gpio.h>
> > +
> > +    clk_gpio_locked: gpio-locked-fixed-clock {
> > +        compatible = "gpio-locked-fixed-clock";
> > +        #clock-cells = <0>;
> > +
> > +        clocks = <&clk0 0>, <&pll 0>;
> > +
> > +        locked-gpios = <&gpio0 4 GPIO_ACTIVE_HIGH>,
> > +                <&gpio0 5 GPIO_ACTIVE_HIGH>,
> > +                <&gpio1 2 GPIO_ACTIVE_LOW>;
> > +
> > +        clock-output-names = "clkout0";
> > +    };
> > 
> > -- 
> > 2.34.1
> > 
> > 
> 

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 228 bytes --]