linux-kernel - Re: [PATCH] dt-bindings: usb: Add binding for Microchip usb5744 hub controller

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Message-ID: <d5763073-3aaa-8a7f-1336-337c125b1a0e@linaro.org>
Date:   Thu, 4 May 2023 09:31:52 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Michal Simek <michal.simek@....com>, linux-kernel@...r.kernel.org,
        monstr@...str.eu, michal.simek@...inx.com, git@...inx.com,
        ilias.apalodimas@...aro.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Piyush Mehta <piyush.mehta@....com>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH] dt-bindings: usb: Add binding for Microchip usb5744 hub
 controller

On 04/05/2023 09:25, Michal Simek wrote:
> 
> 
> On 5/4/23 08:46, Krzysztof Kozlowski wrote:
>> On 03/05/2023 15:39, Michal Simek wrote:
>>> The Microchip usb5744 is a SS/HS USB 3.0 hub controller with 4 ports.
>>> The binding describes USB related aspects of the USB5744 hub, it as
>>> well cover the option of connecting the controller as an i2c slave.
>>> When i2c interface is connected hub needs to be initialized first.
>>> Hub itself has fixed i2c address 0x2D but hardcoding address is not good
>>> idea because address can be shifted by i2c address translator in the
>>> middle.
>>>
>>> Signed-off-by: Piyush Mehta <piyush.mehta@....com>
>>> Signed-off-by: Michal Simek <michal.simek@....com>
>>> ---
>>>
>>> It looks like that usb8041 has also an optional i2c interface which is not
>>> covered. But it is mentioned at commit 40e58a8a7ca6 ("dt-bindings: usb:
>>> Add binding for TI USB8041 hub controller").
>>>
>>> i2c-bus name property was suggested by Rob at
>>> https://lore.kernel.org/all/CAL_JsqJedhX6typpUKbnzV7CLK6UZVjq3CyG9iY_j5DLPqvVdw@mail.gmail.com/
>>> and
>>> https://lore.kernel.org/all/CAL_JsqJZBbu+UXqUNdZwg-uv0PAsNg55026PTwhKr5wQtxCjVQ@mail.gmail.com/
>>>
>>> the question is if adding address like this is acceptable.
>>> But it must be specified.
>>
>> Why? phandle points it explicitly.
> 
> Ok it means just list usb hub on i2c with label and point to it. Works for me.

Right. I missed you want the address of the hub but phandle goes to the
bus. I think listing it on I2C bus (see
arch/arm/boot/dts/vf610-zii-scu4-aib.dts) should work. I think we can
have I2C devices without compatibles.

The problem is that property should have only one definition/type and
i2c-bus is already used in other cases as just "phandle". If we go with
your phandle+address approach, then this should be phandle-array with
items and then we have two different types.

Best regards,
Krzysztof