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

[Ciprian Marian Costea <ciprianmarian.costea@oss.nxp.com>]

On 11/4/2024 5:29 PM, Rob Herring wrote:
> On Wed, Oct 16, 2024 at 06:08:23PM +0200, Alexandre Belloni wrote:
>> On 15/10/2024 16:27:17-0500, Rob Herring wrote:
>>> 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.
>>
>> And in 6 months, we are going to learn that the rtc is used to clock the
>> wifi chip or whatever and we are going to need to add everything in the
>> CCF and we will have an unused property that we are going to have to
>> support forever to avoid breaking the ABI. This already happened...
> 
> For that to happen, the RTC needs to have a clock output. AFAICT, from
> the series it doesn't have any clock output. If it does have an output
> clock, then yes, I would agree with you. But I only know as much as what
> is put here about this h/w.
> 
> Rob

Hello Rob,

Thank you for resuming discussion on this patchset.
Indeed, the RTC does not have a clock output.

In the meantime I've sent a V3 where 'assigned-*' entries are no longer 
required.

Please let me know if V3 is headed into the right direction since I 
prefer not to throw away current 'assigned-*' CCF approach since IMHO 
its scalable with the clock source selection for runtime and suspend.

Ciprian