Hello all,
On 2024-07-18 11:25, Heiko Stübner wrote:
Am Dienstag, 16. Juli 2024, 18:15:08 CEST schrieb Conor Dooley:
On Mon, Jul 15, 2024 at 01:02:49PM +0200, 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@xxxxxxxxx>
> ---
> .../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
Voltage controlled oscillator? Really? That sounds far too similar to
a
VCO to me, and the input voltage here (according to the description at
least) does not affect the frequency of oscillation.
That naming was suggested by Stephen in v1 [0] .
Of course the schematics for the board I have only describe it as
"100MHz,3.3V,3225" , thumbing through some mouser parts matching that
only mentions "supply voltage" in their datasheets but not a dependency
between rate and voltage.
[0]
https://lore.kernel.org/linux-arm-kernel/b3c450a94bcb4ad0bc5b3c7ee8712cb8.sboyd@xxxxxxxxxx/
Why the dedicated binding, rather than adding a supply and enable-gpio
to the existing "fixed-clock" binding? I suspect that a large portion
of
"fixed-clock"s actually require a supply that is (effectively)
always-on.
I guess there are three aspects:
- I do remember discussions in the past about not extending generic
bindings with device-specific stuff. I think generic power-sequences
were the topic back then, though that might have changed over time?
- There are places that describe "fixed-clock" as
"basic fixed-rate clock that cannot gate" [1]
- Stephen also suggested a separate binding [2]
With the fixed-clock being sort of the root for everything else on most
systems, I opted to leave it alone. I guess if the consenus really is
that
this should go there, I can move it, but discussion in v1
Interestingly the fixed clock had a gpios property 10 years ago [3] :-)
.
[1]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/clk/clk-fixed-rate.c#n18
[2]
https://lore.kernel.org/linux-arm-kernel/68f6dc44a8202fd83792e58aea137632.sboyd@xxxxxxxxxx/
[3]
https://lore.kernel.org/linux-kernel//20140515064420.9521.47383@quantum/T/#t
After finally going through the v1 discussion [4] in detail,
here are my further thoughts:
- I agree with dropping the Diodes stuff, [5] because I see
no need for that at this point; though, am I missing
something, where are they actually used?
- I agree that "enable-gpios" and "vdd-supply" should be
required in the binding, [5] because that's the basis for
something to be actually represented this way
- I agree that it should be better not to touch fixed-clock
at this point, simply because it's used in very many places,
and because in this case we need more than it requires (see
the bullet point above)
- As I wrote already, [6] I highly disagree with this being
called voltage-controlled oscillator (VCO), [7] simply
because it isn't a VCO, but a clock that can be gated;
though, looking forward to what the last bullet point
asks to be clarified further
- I still think that gated-clock is the best choice for the
name, because it uses "clock" that's used throughout the
entire codebase, and uses "gated" to reflect the nature
of the clock generator
- Maybe we could actually use fixed-gated-clock as the name,
which would make more sense from the stanpoint of possibly
merging it into fixed-clock at some point, but I'd like
to hear first what's actually going on with the Diodes
stuff that was deleted in v2, which I already asked about
in the first bullet point
[4]
https://lore.kernel.org/linux-rockchip/20240709123121.1452394-1-heiko@xxxxxxxxx/T/#u
[5]
https://lore.kernel.org/linux-rockchip/2e5852b9e94b9a8d0261ce7ad79f4329.sboyd@xxxxxxxxxx/
[6]
https://lore.kernel.org/linux-rockchip/ec84dc37e2c421ee6d31294e08392d57@xxxxxxxxxxx/
[7]
https://lore.kernel.org/linux-rockchip/b3c450a94bcb4ad0bc5b3c7ee8712cb8.sboyd@xxxxxxxxxx/
> +
> +maintainers:
> + - Heiko Stuebner <heiko@xxxxxxxxx>
> +
> +properties:
> + compatible:
> + const: voltage-oscillator
> +
> + "#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 oscillator.
> + maxItems: 1
> +
> + vdd-supply:
> + description: handle of the regulator that provides the supply voltage
> +
> +required:
> + - compatible
> + - "#clock-cells"
> + - clock-frequency
> + - vdd-supply
> +
> +additionalProperties: false
> +
> +examples:
> + - |
> + voltage-oscillator {
> + compatible = "voltage-oscillator";
> + #clock-cells = <0>;
> + clock-frequency = <1000000000>;
> + vdd-supply = <®_vdd>;
> + };
> +...
