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([2401:4900:1f3f:4017:94e1:4956:54cb:7de7]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2656a9caf7dsm66844215ad.133.2025.09.16.05.22.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 16 Sep 2025 05:22:25 -0700 (PDT) Message-ID: <397483db-91de-4ff2-82e3-52ae785bc343@beagleboard.org> Date: Tue, 16 Sep 2025 17:52:18 +0530 Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: Device tree representation of (hotplug) connectors: discussion at ELCE To: Geert Uytterhoeven , Herve Codina Cc: David Gibson , Luca Ceresoli , Krzysztof Kozlowski , devicetree@vger.kernel.org, Rob Herring , Jason Kridner , Krzysztof Kozlowski , Conor Dooley , devicetree-compiler@vger.kernel.org, linux-kernel@vger.kernel.org, Thomas Petazzoni , Andrew Davis , Wolfram Sang References: <20250902105710.00512c6d@booty> <337281a8-77f9-4158-beef-ae0eda5000e4@beagleboard.org> <20250908145155.4f130aec@bootlin.com> <20250909114126.219c57b8@bootlin.com> <20250911104828.48ef2c0e@bootlin.com> <20250916084631.77127e29@bootlin.com> Content-Language: en-US From: Ayush Singh In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 9/16/25 15:44, Geert Uytterhoeven wrote: > Hi Hervé, > > On Tue, 16 Sept 2025 at 08:46, Herve Codina wrote: >> On Mon, 15 Sep 2025 14:51:41 +1000 >> David Gibson wrote: >>> On Thu, Sep 11, 2025 at 10:48:28AM +0200, Herve Codina wrote: >>>> From the addon board point of view, the only think we can >>>> say is "me, as an addon board, I need a connector of type 'foo' and a >>>> connector of type 'bar'". >>> Agreed. >>> >>>> Also, at base board level, statically defined in the DT >>>> connA is described (type 'foo'), connB and connC are >>>> described (type 'bar'). >>>> >>>> The choice to map connA to the type 'foo' connector expected by the addon >>>> and the choice to map connB or connC to the type 'bar' connector expected by >>>> the addon can only be done at runtime and probably with the help of a driver >>>> that have the knowledge of the 3 connectors. >>> Agreed. >>> >>>> I have the feeling that the choice of physical connectors to which the addon >>>> board is connected to is a human choice when the board is connected. >>> Yes. Although if the addons have an EEPROM, or some other sort of ID >>> register, it may be possible for some connector drivers to probe this. >> Right, I think we agree that a driver is needed to help in the mapping at >> least when multiple connectors are involved. > I agree you need a driver to read an ID EEPROM. > But why would you need a driver if no ID EEPROM is involved? > If the connector types on base board and add-on match, it should work. > > Gr{oetje,eeting}s, > > Geert > How would a connector be disabled in such a setup? I guess maybe status property can be used while applying overlay to check if the connector is enabled. But maybe that goes outside the scope of fdtoverlay? Also, I would assume that most such connectors would want to provide some kind of configfs based API to add/remove addon boards. Best Regards, Ayush Singh