linux-kernel - Re: [PATCH v5 3/5] arm64: dts: ti: k3-j784s4: Add WIZ and SERDES PHY nodes

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Date:   Thu, 20 Jul 2023 15:06:03 +0530
From:   Jayesh Choudhary <j-choudhary@...com>
To:     Nishanth Menon <nm@...com>, Andrew Davis <afd@...com>
CC:     <vigneshr@...com>, <krzysztof.kozlowski+dt@...aro.org>,
        <s-vadapalli@...com>, <kristo@...nel.org>, <robh+dt@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 3/5] arm64: dts: ti: k3-j784s4: Add WIZ and SERDES PHY
 nodes



On 14/07/23 00:28, Nishanth Menon wrote:
> On 13:31-20230713, Andrew Davis wrote:
>> On 7/13/23 1:21 PM, Nishanth Menon wrote:
>>> On 21:01-20230713, Jayesh Choudhary wrote:
>>>>
>>>>
>>>> On 12/07/23 19:48, Nishanth Menon wrote:
>>>>> On 15:47-20230710, Jayesh Choudhary wrote:
>>>>>> From: Siddharth Vadapalli <s-vadapalli@...com>
>>>>>>
>>>>>> J784S4 SoC has 4 Serdes instances along with their respective WIZ
>>>>>> instances. Add device-tree nodes for them and disable them by default.
>>>>>>
>>>>>> Signed-off-by: Siddharth Vadapalli <s-vadapalli@...com>
>>>>>> [j-choudhary@...com: fix serdes_wiz clock order]
>>>>>> Signed-off-by: Jayesh Choudhary <j-choudhary@...com>
>>>>>> ---
>>>>> NAK. This patch introduces the following dtbs_check warning.
>>>>> arch/arm64/boot/dts/ti/k3-am69-sk.dtb: serdes-refclk: 'clock-frequency' is a required property
>>>>>
>>>>
>>>> Sorry for this. This property was added in the final board file.
>>>> I will fix it in the next revision.
>>>> I will add '0' as clock-property in the main file similar to j721e[1]
>>>> which will be overridden in the board file with required value to get
>>>> rid of this warning.
>>>
>>> That would follow what renesas (r8a774a1.dtsi) and imx
>>> (imx8dxl-ss-conn.dtsi) seem to be doing as well. Just make sure to add
>>> documentation to the property to indicate expectation. Unless someone
>>> has objections to this approach.
>>>
>>
>> Would it work better to disable these nodes, only enabling them in the
>> board files when a real clock-frequency can be provided?
>>
>> My initial reaction would be to move the whole external reference clock
>> node to the board file since that is where it is provided, but seems
>> that would cause more churn in serdes_wiz* nodes than we would want..
> 
> I would prefer that as well, but I have'nt gone around looking for
> similar examples on other SoCs (Jayesh, can you check?). One other
> approach (alipine and few other places) has been for the bootloader to
> update the property set in dtb as 0, which is not needed in this case
> to the best of what I see.. just hoping we use a technique that most
> board folks are familiar with across SoCs.
> 


I can see the clock nodes in board files for some vendors. But like
Andrew said, that would cause issues with serdes_wiz node in the
main.dtsi.

So I think it would be better to keep the external clock node in main
dtsi itself. I will add comments to the property to indicate that this
value will be over-written in board dts.
Posting v6 to address these comments and others on the series.

Thanks,
Jayesh