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Date: Wed, 20 Dec 2023 18:07:53 +0800
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Subject: Re: [PATCH v2 5/5] dt-bindings: net: ipq4019-mdio: Document ipq5332
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To: Conor Dooley <conor@kernel.org>
CC: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>, <agross@kernel.org>,
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From: Jie Luo <quic_luoj@quicinc.com>
In-Reply-To: <20231219-childcare-sugar-d1ecde8bd0b0@spud>
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On 12/19/2023 11:47 PM, Conor Dooley wrote:
> On Sat, Dec 16, 2023 at 11:37:08PM +0800, Jie Luo wrote:
>> On 12/16/2023 10:16 PM, Conor Dooley wrote:
>>> On Sat, Dec 16, 2023 at 09:16:49PM +0800, Jie Luo wrote:
>>>> On 12/15/2023 9:41 PM, Conor Dooley wrote:
>>>>> On Fri, Dec 15, 2023 at 08:40:20PM +0800, Jie Luo wrote:
>>>>>> On 12/15/2023 8:19 PM, Krzysztof Kozlowski wrote:
>>>>>>> On 15/12/2023 12:42, Jie Luo wrote:
> 
>>>>>> There is also no enable control for the reference clocks since it is
>>>>>> inputted by the hardware PIN connection, i will update these description
>>>>>> in the DT to make it more clear.
>>>>>
>>>>> Again, this does not justify having custom properties for this clock,
>>>>> as it is no different to other platforms. As far as I can tell, the only
>>>>> thing that a standard "clocks" property cannot convey here is the
>>>>> internal reference. I would suggest that since there is only one
>>>>> internal clock frequency, the absence of this particular clock in the
>>>>> "clocks" property can be used to determine that the reference is the
>>>>> internal on
>>>
>>> I'm surprised you didn't pick up on this, but there are actually _2_
>>> internal references, which I have just noticed while double checking the
>>> binding patch.
>>
>> i noticed this, the reference clock source can be supported by clocks as
>> you suggested here, it is really helpful.
>>
>>> What is the impact of using the 48 MHz or 96 MHz internal reference?
>> They works on the different IPQ platform, 96MHZ internal reference is
>> used on IPQ5018, the internal 48MHZ is used on the IPQ5332, that is
>> same as what you describe above, the different clock source rate is
>> selected as the different register value, then the PLL can do the
>> corresponding config to output the correct clock rate, the external
>> clock source is also same if the clock rate is same, just the different
>> hardware PIN is selected if the external reference source is configured.
> 
> 
> Ah, so there is only one internal reference frequency per device. Then
> my suggestion to use the presence of the clock in the clocks property
> should work, just the fallback to the internal reference is going to
> depend on the compatible.
> 
> Thanks,
> Conor.

The reference clock source is configurable, normally there is the fix
reference clock configured per each IPQ platform, but we should keep
the reference clock source configurable in case of the reference clock
source switch needed in the future.

you are right, the reference clock source can be distinguished by
checking the clock rate and the compatible string.