linux-kernel - Re: [PATCH v3 05/12] dt-bindings: phy: renesas,usb2-phy: Add renesas,sysc-signals

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Message-ID: <4a07048a-c55a-4fd3-b4e5-7f9d218de76f@kernel.org>
Date: Thu, 22 May 2025 14:46:40 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Claudiu Beznea <claudiu.beznea@...on.dev>
Cc: vkoul@...nel.org, kishon@...nel.org, robh@...nel.org, krzk+dt@...nel.org,
 conor+dt@...nel.org, p.zabel@...gutronix.de, geert+renesas@...der.be,
 magnus.damm@...il.com, yoshihiro.shimoda.uh@...esas.com, kees@...nel.org,
 gustavoars@...nel.org, biju.das.jz@...renesas.com,
 linux-phy@...ts.infradead.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
 linux-hardening@...r.kernel.org, john.madieu.xa@...renesas.com,
 Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH v3 05/12] dt-bindings: phy: renesas,usb2-phy: Add
 renesas,sysc-signals

On 22/05/2025 12:26, Claudiu Beznea wrote:
> Hi, Krzysztof,
> 
> On 22.05.2025 10:03, Krzysztof Kozlowski wrote:
>> On Wed, May 21, 2025 at 05:09:36PM GMT, Claudiu wrote:
>>>  .../bindings/phy/renesas,usb2-phy.yaml        | 22 +++++++++++++++++++
>>>  1 file changed, 22 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/phy/renesas,usb2-phy.yaml b/Documentation/devicetree/bindings/phy/renesas,usb2-phy.yaml
>>> index 12f8d5d8af55..e1e773cba847 100644
>>> --- a/Documentation/devicetree/bindings/phy/renesas,usb2-phy.yaml
>>> +++ b/Documentation/devicetree/bindings/phy/renesas,usb2-phy.yaml
>>> @@ -86,6 +86,16 @@ properties:
>>>  
>>>    dr_mode: true
>>>  
>>> +  renesas,sysc-signals:
>>> +    description: System controller phandle, specifying the register
>>> +      offset and bitmask associated with a specific system controller signal
>>
>> This is 100% redundant information. system controller specifying system
>> controller signal.
>>
>> Drop.
>>
>>
>>> +    $ref: /schemas/types.yaml#/definitions/phandle-array
>>> +    items:
>>> +      - items:
>>> +          - description: system controller phandle
>>
>> What for? Explain the usage. How is ut used by this hardware.
> 
> OK, I though I've explained in the renesas,sysc-signals description
> section. I'll adjust it and move it here.

That description did not explain me at all. I mean really, which parts
explains the usage by hardware?


> 
>>
>>> +          - description: register offset associated with a signal
>>
>> What signal? That's a phy.
> 
> Would you like me to specify here exactly the signal name? I tried to made
> it generic as the system controller provides other signals to other IPs,
> the intention was to use the same property for other IPs, if any. And kept
> it generic in the idea it could be used in future, if any, for other
> signals provided by the system controller to the USB PHY.

Bindings are not generic, so yes, you must explain here what hardware
aspect this is relevant to. What signal? Between whom?

> 
> As explained in the commit description, on the Renesas RZ/G3S SoC, the USB
> PHY receives a signal from the system controller that need to be

Interrupt? Some pin changes state? What is a signal? This property is in
the USB PHY device, not system controller.

> de-asserted/asserted when power is turned on/off. This signal, called
> PWRRDY, is controlled through a specific register in the system controller
> memory space.
> 
> With this property the intention is to specify to the USB PHY driver the
> phandle to the SYSC, register offset within SYSC address space in charge of

This is obvious from the schema and I asked to drop redundant parts.

> controlling the USB PWRRDY signal and the bitmask within this register.

So basically this last piece describes what this hardware needs to do
with system controller? Change some register?

> 
> The PHY driver parse this information and set the signal at proper moments.
> 
> 
>>
>>> +          - description: register bitmask associated with a signal
>>> +
>>>  if:
>>>    properties:
>>>      compatible:
>>> @@ -117,6 +127,18 @@ allOf:
>>>        required:
>>>          - resets
>>>  
>>> +  - if:
>>> +      properties:
>>> +        compatible:
>>> +          contains:
>>> +            const: renesas,usb2-phy-r9a08g045
>>> +    then:
>>> +      required:
>>> +        - renesas,sysc-signals
>>
>> That's ABI break.
> 
> There is no in kernel device tree users of "renesas,usb2-phy-r9a08g045"
> compatible. It is introduced in patch 11/12 from this series. With this do
> you still consider it ABI break?

Then this patch cannot be split from binding introducing the user. Don't
add unused/undocumented compatibles.



Best regards,
Krzysztof