On Thu, Jul 18, 2024 at 11:25:28AM +0200, Heiko Stübner wrote: > Hi Conor, > > 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] . I think "voltage-oscillator" is a confusing name, and having "voltage controlled oscillator" in the title doubly so as this isn't a binding for a VCO. A VCO is a more general case of the sort of device that you're talking about here, so a part of me can see it - but I think specific compatibles would be required for actual VCOs, since the "transfer function" would vary per device. > 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. FWIW, I wouldn't classify this as device-specific. "enable-gpios" and "vdd-supply" are pretty generic and I think the latter is missing from the vast majority of real* "fixed-clocks". I would expect that devices where the datasheet would call * Real because there's plenty of "fixed-clocks" (both in and out of tree) that are used to work around the lack of a clock-controller driver for an SoC. > 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] I think that that is something that could be changed, it's "just" a comment in some code! Sounds like Stephen disagrees though :) > - Stephen also suggested a separate binding [2] I liked your "gated-oscillator" suggestion in another reply, but "gated-fixed-clock" might be a better "thematic" fit since this is a special case of fixed-clocks? Cheers, Conor. > 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] :-) . heh! > > [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
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