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SubjectRe: [RFC PATCH 3/3] net: phy: at803x: add device tree binding
Am 2019-10-31 18:35, schrieb Florian Fainelli:
> On 10/31/19 10:22 AM, Michael Walle wrote:
>> Am 2019-10-31 00:59, schrieb Michael Walle:
>>>>> +
>>>>> +    if (of_property_read_bool(node, "atheros,keep-pll-enabled"))
>>>>> +        priv->flags |= AT803X_KEEP_PLL_ENABLED;
>>>>
>>>> This should probably be a PHY tunable rather than a Device Tree
>>>> property
>>>> as this delves more into the policy than the pure hardware
>>>> description.
>>>
>>> To be frank. I'll first need to look into PHY tunables before
>>> answering ;)
>>> But keep in mind that this clock output might be used anywhere on the
>>> board. It must not have something to do with networking. The PHY has
>>> a
>>> crystal and it can generate these couple of frequencies regardless of
>>> its network operation.
>>
>> Although it could be used to provide any clock on the board, I don't
>> know
>> if that is possible at the moment, because the PHY is configured in
>> config_init() which is only called when someone brings the interface
>> up,
>> correct?
>>
>> Anyway, I don't know if that is worth the hassle because in almost all
>> cases the use case is to provide a fixed clock to the MAC for an RGMII
>> interface. I don't know if that really fits a PHY tunable, because in
>> the worst case the link won't work at all if the SoC expects an
>> always-on clock.
>
> Well, that was my question really, is the clock output being controlled
> the actual RXC that will feed back to the MAC or is this is another
> clock output pin (sorry if you indicated that before and I missed it)?

No it is not the RX clock. The PHY has three clock pins, RX clock, TX
clock and a general purpose CLK_25M pin.

> If this is the PHY's RXC, then does the configuration (DSP, PLL, XTAL)
> matter at all on the generated output frequency, or is this just a
> choice for the board designer, and whether the PHY is configured for
> MII/RGMII, it outputs the appropriate clock at 25/125Mhz?

The RXC changes the frequency according to the speed.

--
-michael

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