Re: [PATCH v2 5/5] dt-bindings: net: ipq4019-mdio: Document ipq5332 platform

[Jie Luo]

On 12/15/2023 6:37 PM, Krzysztof Kozlowski wrote:
> On 15/12/2023 11:33, Jie Luo wrote:
> > > > > > > > > > +  cmn-reference-clock:
> > > > > > > > > > +    oneOf:
> > > > > > > > > > +      - items:
> > > > > > > > > > +          - enum:
> > > > > > > > > > +              - 0   # CMN PLL reference internal 48MHZ
> > > > > > > > > > +              - 1   # CMN PLL reference external 25MHZ
> > > > > > > > > > +              - 2   # CMN PLL reference external 31250KHZ
> > > > > > > > > > +              - 3   # CMN PLL reference external 40MHZ
> > > > > > > > > > +              - 4   # CMN PLL reference external 48MHZ
> > > > > > > > > > +              - 5   # CMN PLL reference external 50MHZ
> > > > > > > > > > +              - 6   # CMN PLL reference internal 96MHZ
> > > > > > > > >
> > > > > > > > > Why is this not represented by an element of the clocks property?
> > > > > > > >
> > > > > > > > This property is for the reference clock source selection of CMN PLL,
> > > > > > > > CMN PLL generates the different clock rates for the different Ethernet
> > > > > > > > blocks, this CMN PLL configuration is not located in the GCC, so the
> > > > > > > > clock framework can't be used, which is the general hardware register
> > > > > > > > instead of RCG register for GCC.
> > > > > > >
> > > > > > > I don't see how the clock being provided by the "GCC" (whatever that is)
> > > > > > > or by some other clock controller or fixed clock makes a difference.
> > > > > > > Why can't the other clock provider be represented in the devicetree?
> > > > > >
> > > > > > cmn-reference-clock is for selecting the reference clock source for the
> > > > > > whole Ethernet block, which is just the standalone configure register.
> > > > >
> > > > > Sure, you are aware though that all clocks are just configure registers?
> > > > >
> > > > > Which clocks are these mentioned in the property? From where do they come?
> > > > >
> > > > > Anyway, property is in existing form is not correct - this is not a
> > > > > generic property.
> > > >
> > > > This property cmn-reference-clock is just the hardware register
> > > > configuration, since the different IPQ platform needs to select
> > > > the different reference clock source for the CMN PLL block that
> > > > provides the various clock outputs to the all kinds of Ethernet
> > > > devices, which is not from GCC provider.
> > >
> > > AGAIN: where do the clocks come from? Which device generates them?
> >
> > Oh, OK, the reference clock is from wifi that provides 48MHZ to
> > Ethernet block.
>
> Then WiFi should be providing you the clock and this device should be
> clock consumer, right?

Yes, wifi provides 48MHz clock to CMM PLL block, there is no GCC
for this 48MHZ clock output, it is the hardware PIN connection.
> Best regards,
> Krzysztof