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([2600:8803:e7e4:1d00:7648:43db:38fd:de4a]) by smtp.gmail.com with ESMTPSA id 006d021491bc7-61bebf8d16dsm671683eaf.1.2025.08.17.09.51.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 17 Aug 2025 09:51:24 -0700 (PDT) Message-ID: <8e228d2d-d22f-4092-8c6d-94ce989b4a84@baylibre.com> Date: Sun, 17 Aug 2025 11:51:22 -0500 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/5] dt-bindings: iio: mcp9600: Add compatible for microchip,mcp9601 To: Jonathan Cameron , Ben Collins , =?UTF-8?Q?Nuno_S=C3=A1?= , Andy Shevchenko , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Andrew Hepp , linux-iio@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org References: <20250815164627.22002-1-bcollins@watter.com> <20250815164627.22002-2-bcollins@watter.com> <20250816105825.35e69652@jic23-huawei> <66063382-78c6-4d93-be25-46e972e390f4@baylibre.com> <2025081711-coral-aardwark-9f061b@boujee-and-buff> Content-Language: en-US From: David Lechner In-Reply-To: <2025081711-coral-aardwark-9f061b@boujee-and-buff> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/17/25 11:37 AM, Ben Collins wrote: > On Sat, Aug 16, 2025 at 01:55:31PM -0500, David Lechner wrote: >> On 8/16/25 4:58 AM, Jonathan Cameron wrote: >>> On Fri, 15 Aug 2025 16:46:03 +0000 >>> Ben Collins wrote: >>> >>>> The mcp9600 driver supports the mcp9601 chip, but complains about not >>>> recognizing the device id on probe. A separate patch... >>>> >>>> iio: mcp9600: Recognize chip id for mcp9601 >>>> >>>> ...addresses this. This patch updates the dt-bindings for this chip to >>>> reflect the change to allow explicitly setting microchip,mcp9601 as >>>> the expected chip type. >>>> >>>> The mcp9601 also supports features not found on the mcp9600, so this >>>> will also allow the driver to differentiate the support of these >>>> features. >>> >>> If it's additional features only then you can still use a fallback >>> compatible. Intent being that a new DT vs old kernel still 'works'. >>> >>> Then for the driver on new kernels we match on the new compatible and >>> support those new features. Old kernel users get to keep the ID >>> mismatch warning - they can upgrade if they want that to go away ;) >>> >>> Krzysztof raised the same point on v2 but I'm not seeing it addressed >>> in that discussion. >> >> One could make the argument that these are not entirely fallback >> compatible since bit 4 of the STATUS register has a different >> meaning depending on if the chip is MCP9601/L01/RL01 or not. > > There are some nuances to this register between the two, but it can be > used generically as "not in range" for both. > > My understanding from the docs is if VSENSE is connected on mcp9601, > then it is explicitly open-circuit detection vs. short-circuit, which > is bit 5. > >> Interestingly, the existing bindings include interrupts for >> open circuit and short circuit alert pins. But these pins >> also only exist on MCP9601/L01/RL01. If we decide these aren't >> fallback compatible, then those properties should have the >> proper constraints added as well. > > In my v4 patch, I'm going to remove the short/open circuit interrupts > since they are not implemented, yet. Don't remove them from the devicetree bindings. Even if the Linux driver doesn't use it, the bindings should be as complete as possible. https://docs.kernel.org/devicetree/bindings/writing-bindings.html > > I have VSENSE wired on my board so I can work on those interrupts and > register support in a later patch series. >