linux-kernel - Re: [PATCH v8 02/11] dt-bindings: rtc: sun6i: Add H616 compatible string

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Date:   Mon, 2 Aug 2021 01:39:38 +0100
From:   Andre Przywara <andre.przywara@....com>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Rob Herring <robh@...nel.org>, Icenowy Zheng <icenowy@...c.io>,
        Samuel Holland <samuel@...lland.org>,
        linux-arm-kernel@...ts.infradead.org, linux-sunxi@...glegroups.com,
        linux-sunxi@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Ondrej Jirman <megous@...ous.com>, devicetree@...r.kernel.org,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        linux-rtc@...r.kernel.org
Subject: Re: [PATCH v8 02/11] dt-bindings: rtc: sun6i: Add H616 compatible
 string

On Mon, 26 Jul 2021 16:41:37 +0200
Maxime Ripard <maxime@...no.tech> wrote:

> Hi,
> 
> On Fri, Jul 23, 2021 at 04:38:29PM +0100, Andre Przywara wrote:
> > Add the obvious compatible name to the existing RTC binding.
> > The actual RTC part of the device uses a different day/month/year
> > storage scheme, so it's not compatible with the previous devices.
> > Also the clock part is quite different, as there is no external 32K LOSC
> > oscillator input.
> > 
> > Signed-off-by: Andre Przywara <andre.przywara@....com>
> >
> > ---
> >  .../bindings/rtc/allwinner,sun6i-a31-rtc.yaml      | 14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/rtc/allwinner,sun6i-a31-rtc.yaml b/Documentation/devicetree/bindings/rtc/allwinner,sun6i-a31-rtc.yaml
> > index beeb90e55727..d8a6500e5840 100644
> > --- a/Documentation/devicetree/bindings/rtc/allwinner,sun6i-a31-rtc.yaml
> > +++ b/Documentation/devicetree/bindings/rtc/allwinner,sun6i-a31-rtc.yaml
> > @@ -26,6 +26,7 @@ properties:
> >            - const: allwinner,sun50i-a64-rtc
> >            - const: allwinner,sun8i-h3-rtc
> >        - const: allwinner,sun50i-h6-rtc
> > +      - const: allwinner,sun50i-h616-rtc
> >  
> >    reg:
> >      maxItems: 1
> > @@ -104,6 +105,19 @@ allOf:
> >            minItems: 3
> >            maxItems: 3
> >  
> > +  - if:
> > +      properties:
> > +        compatible:
> > +          contains:
> > +            const: allwinner,sun50i-h616-rtc
> > +
> > +    then:
> > +      properties:
> > +        clock-output-names:
> > +          minItems: 3
> > +          maxItems: 3  
> 
> You don't need both of them when they are equal
> 
> > +        clocks: false
> > +  
> 
> It's not entirely clear to me what those clocks are about though. If we
> look at the clock output in the user manual, it looks like there's only
> two clocks that are actually being output: the 32k "fanout" clock and
> the losc. What are the 3 you're talking about?]

I see three: the raw SYSTEM "CLK32K_LOSC", the RTC input + debounce
clock (/32), and the multiplexed PAD.

> Also, it looks like the 32k fanout clock needs at least the hosc or
> pll-periph in input, so we probably don't want to ask for no parent
> clock?

Well, we never seem to reference the HOSC this way, this was always
somewhat explicit. And yes, there is PLL-PERIPH as an input, but we
don't support this yet. So I went with 0 input clocks *for now*: the
driver can then ignore all clocks, so any clock referenced in the DT
later won't cause any harm. This will all be addressed by Samuel's RTC
clock patch, which will also touch the H6, IIRC. And it looks like we
will need to touch the binding anyway then, but can then just *extend*
this.

The point is that everything works(TM) as of now: The consumers
(pinctrl) get their LOSC clock, and can go ahead. This is in the
interest to get us moving now, and refine the actual implementation
later. In this case this will only change the accuracy of the LOSC
frequency (HOSC/x, PLL/y, calibrated RC), but won't change the
semantics.

Cheers,
Andre