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([2401:4900:1f3f:4017:94e1:4956:54cb:7de7]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-32dd98b3e8fsm18103613a91.17.2025.09.16.08.35.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 16 Sep 2025 08:35:28 -0700 (PDT) Message-ID: <3b5b1b77-97fa-4eab-b5ec-7b4b7099c87d@beagleboard.org> Date: Tue, 16 Sep 2025 21:05:23 +0530 Precedence: bulk X-Mailing-List: devicetree-compiler@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 Cc: Herve Codina , 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> <397483db-91de-4ff2-82e3-52ae785bc343@beagleboard.org> Content-Language: en-US From: Ayush Singh In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 9/16/25 19:04, Geert Uytterhoeven wrote: > Hi Ayush, > > On Tue, 16 Sept 2025 at 14:22, Ayush Singh wrote: >> On 9/16/25 15:44, Geert Uytterhoeven wrote: >>> 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. >> 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? > Why would you want to disable a connector? So a lot of embedded SoCs (eg. TI AM6254 [0]) have co-processors (M4F in case of AM6254). These co-processors can run full blow RTOS (most BeagleBoard boards like PocketBeagle 2 [1] have Zephyr support). When using a peripheral from the co-processor running such RTOS, it needs to be disabled on Linux side. > >> Also, I would assume that most such connectors would want to provide >> some kind of configfs based API to add/remove addon boards. > Yes, we need some way to configure add-on board add/remove, > and on which connector(s). > > Gr{oetje,eeting}s, > > Geert > Best Regards Ayush Singh [0]: https://www.ti.com/product/AM625 [1]: https://www.ti.com/product/AM625