linux-kernel - Re: [PATCH 2/2] dt-bindings: usb: ti,usb8041: Add binding for TI USB8044 hub controller

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Message-ID: <d4604713-ffb3-4cb2-bcd8-14c0519ad608@topic.nl>
Date: Fri, 9 May 2025 07:56:35 +0200
From: Mike Looijmans <mike.looijmans@...ic.nl>
To: Conor Dooley <conor@...nel.org>
CC: linux-usb@...r.kernel.org,
 Alexander Stein <alexander.stein@...tq-group.com>,
 Conor Dooley <conor+dt@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] dt-bindings: usb: ti,usb8041: Add binding for TI
 USB8044 hub controller

On 08-05-2025 17:53, Conor Dooley wrote:
> On Thu, May 08, 2025 at 05:19:03PM +0200, Mike Looijmans wrote:
>> On 08-05-2025 16:58, Conor Dooley wrote:
>>> On Wed, May 07, 2025 at 03:11:43PM +0200, Mike Looijmans wrote:
>>>> The TI USB8044 is similar to the USB8041.
>>> Similar how? Why's a fallback not suitable?
>> I don't quite understand what is meant by "fallback" here?
> A fallback compatible, since you;re using the same match data as the
> 8041.

I think it would work. It would look strange though, having to put an 
additional vid/pid in the devicetree to make it work.


>> It's similar in that the USB8044 provides the same functionality and can use
>> the same driver as the USB8041, all that is needed is to add the PID/VID
>> values.
> Is this onboard_dev_id_table table with the vid/pid used in combination
> with dt, or in-place of dt when device detection is dynamic? If the
> latter, why can't dt use a fallback compatible since the handling is
> identical to the 8041?

My basic understanding is:

The devicetree match creates a platform device that controls the reset 
pin of the hub. It's basic task is to de-assert the reset, so the hub 
starts negotiating. This part also works with the 8041 devicetree entry 
(which is how I first tried to get it up and running).

The VID/PID table then matches the hub on the USB bus, which can then be 
associated with its platform device. Since the 8044 reports a different 
VID/PID, this part only worked when I added the entries to the tables.

-- 
Mike Looijmans