Re: [PATCH v2 1/4] dt-bindings: rtc: add schema for NXP S32G2/S32G3 SoCs

[Rob Herring <robh@kernel.org>]

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@oss.nxp.com>
> > 
> > This patch adds the dt-bindings for NXP S32G2/S32G3 SoCs RTC driver.
> > 
> > Co-developed-by: Bogdan-Gabriel Roman <bogdan-gabriel.roman@nxp.com>
> > Signed-off-by: Bogdan-Gabriel Roman <bogdan-gabriel.roman@nxp.com>
> > Co-developed-by: Ghennadi Procopciuc <ghennadi.procopciuc@nxp.com>
> > Signed-off-by: Ghennadi Procopciuc <ghennadi.procopciuc@nxp.com>
> > Signed-off-by: Ciprian Marian Costea <ciprianmarian.costea@oss.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@nxp.com>
> > +  - Ciprian Marian Costea <ciprianmarian.costea@nxp.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@40060000 {
> > +        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