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Message-ID: <20241015212717.GA1983714-robh@kernel.org>
Date: Tue, 15 Oct 2024 16:27:17 -0500
From: Rob Herring <robh@...nel.org>
To: Ciprian Costea <ciprianmarian.costea@....nxp.com>
Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>,
Krzysztof Kozlowski <krzk+dt@...nel.org>,
Conor Dooley <conor+dt@...nel.org>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>, linux-rtc@...r.kernel.org,
devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org,
NXP S32 Linux Team <s32@....com>,
Christophe Lizzi <clizzi@...hat.com>,
Alberto Ruiz <aruizrui@...hat.com>,
Enric Balletbo <eballetb@...hat.com>,
Bogdan-Gabriel Roman <bogdan-gabriel.roman@....com>,
Ghennadi Procopciuc <ghennadi.procopciuc@....com>
Subject: Re: [PATCH v2 1/4] dt-bindings: rtc: add schema for NXP S32G2/S32G3
SoCs
On Tue, Oct 15, 2024 at 04:15:40PM -0500, Rob Herring wrote:
> On Tue, Oct 15, 2024 at 01:51:30PM +0300, Ciprian Costea wrote:
> > From: Ciprian Marian Costea <ciprianmarian.costea@....nxp.com>
> >
> > This patch adds the dt-bindings for NXP S32G2/S32G3 SoCs RTC driver.
> >
> > Co-developed-by: Bogdan-Gabriel Roman <bogdan-gabriel.roman@....com>
> > Signed-off-by: Bogdan-Gabriel Roman <bogdan-gabriel.roman@....com>
> > Co-developed-by: Ghennadi Procopciuc <ghennadi.procopciuc@....com>
> > Signed-off-by: Ghennadi Procopciuc <ghennadi.procopciuc@....com>
> > Signed-off-by: Ciprian Marian Costea <ciprianmarian.costea@....nxp.com>
> > ---
> > .../devicetree/bindings/rtc/nxp,s32g-rtc.yaml | 102 ++++++++++++++++++
> > 1 file changed, 102 insertions(+)
> > create mode 100644 Documentation/devicetree/bindings/rtc/nxp,s32g-rtc.yaml
> >
> > diff --git a/Documentation/devicetree/bindings/rtc/nxp,s32g-rtc.yaml b/Documentation/devicetree/bindings/rtc/nxp,s32g-rtc.yaml
> > new file mode 100644
> > index 000000000000..3a77d4dd8f3d
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/rtc/nxp,s32g-rtc.yaml
> > @@ -0,0 +1,102 @@
> > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/rtc/nxp,s32g-rtc.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: NXP S32G2/S32G3 Real Time Clock (RTC)
> > +
> > +maintainers:
> > + - Bogdan Hamciuc <bogdan.hamciuc@....com>
> > + - Ciprian Marian Costea <ciprianmarian.costea@....com>
> > +
> > +properties:
> > + compatible:
> > + oneOf:
> > + - enum:
> > + - nxp,s32g2-rtc
> > + - items:
> > + - const: nxp,s32g3-rtc
> > + - const: nxp,s32g2-rtc
> > +
> > + reg:
> > + maxItems: 1
> > +
> > + interrupts:
> > + maxItems: 1
> > +
> > + "#clock-cells":
> > + const: 1
> > +
> > + clocks:
> > + items:
> > + - description: ipg clock drives the access to the
> > + RTC iomapped registers
> > +
> > + clock-names:
> > + items:
> > + - const: ipg
> > +
> > + assigned-clocks:
> > + minItems: 1
> > + items:
> > + - description: Runtime clock source. It must be a clock
> > + source for the RTC module. It will be disabled by hardware
> > + during Standby/Suspend.
> > + - description: Standby/Suspend clock source. It is optional
> > + and can be used in case the RTC will continue ticking during
> > + platform/system suspend. RTC hardware module contains a
> > + hardware mux for clock source selection.
>
> If the RTC h/w contains a mux, then your mux inputs should be listed in
> 'clocks', not here.
>
> > +
> > + assigned-clock-parents:
> > + description: List of phandles to each parent clock.
> > +
> > + assigned-clock-rates:
> > + description: List of frequencies for RTC clock sources.
> > + RTC module contains 2 hardware divisors which can be
> > + enabled or not. Hence, available frequencies are the following
> > + parent_freq, parent_freq / 512, parent_freq / 32 or
> > + parent_freq / (512 * 32)
>
> In general, assigned-clocks* do not need to be documented and should
> never be required.
>
> > +
> > +required:
> > + - compatible
> > + - reg
> > + - interrupts
> > + - "#clock-cells"
> > + - clocks
> > + - clock-names
> > + - assigned-clocks
> > + - assigned-clock-parents
> > + - assigned-clock-rates
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > + - |
> > + #include <dt-bindings/interrupt-controller/arm-gic.h>
> > + #include <dt-bindings/interrupt-controller/irq.h>
> > +
> > + rtc0: rtc@...60000 {
> > + compatible = "nxp,s32g3-rtc",
> > + "nxp,s32g2-rtc";
> > + reg = <0x40060000 0x1000>;
> > + interrupts = <GIC_SPI 121 IRQ_TYPE_LEVEL_HIGH>;
> > + #clock-cells = <1>;
> > + clocks = <&clks 54>;
> > + clock-names = "ipg";
> > + /*
> > + * Configuration of default parent clocks.
> > + * 'assigned-clocks' 0-3 IDs are Runtime clock sources
> > + * 4-7 IDs are Suspend/Standby clock sources.
> > + */
> > + assigned-clocks = <&rtc0 2>, <&rtc0 4>;
>
> That's weird...
>
> > + assigned-clock-parents = <&clks 56>, <&clks 55>;
>
> I'd expect these should be in 'clocks'. I don't think this node should
> be a clock provider unless it provides a clock to something outside the
> RTC.
>
> Looks like you are just using assigned-clocks to configure the clock mux
> in the RTC. That's way over complicated. Just define a vendor specific
> property with the mux settings.
I just read v1 and got told use the clock framework...
I disagree completely. Tons of h/w blocks have the ability to select
(internal to the block) from multiple clock sources. Making the block a
clock provider to itself is completely pointless and an overkill, and
we *never* do that. Any display controller or audio interface has
mutiple clock sources as just 2 examples.
However, I don't see why you need the divider config in DT. Can't you
figure out what divider you need based on input frequency? The output
frequency should be fixed, right?
Rob
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