linux-kernel - Re: [PATCH] i2c: muxes: pca954x: Fix broken reset-gpio usage

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Message-ID: <69ef304b-491a-4434-97c1-97eccd99ea66@linaro.org>
Date: Mon, 3 Nov 2025 16:36:29 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Peter Rosin <peda@...ntia.se>, Philipp Zabel <p.zabel@...gutronix.de>,
 Wojciech Siudy <wojciech.siudy@...ia.com>,
 Wolfram Sang <wsa+renesas@...g-engineering.com>, linux-i2c@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i2c: muxes: pca954x: Fix broken reset-gpio usage

On 03/11/2025 16:19, Krzysztof Kozlowski wrote:
> Revert commit 690de2902dca ("i2c: muxes: pca954x: Use reset controller
> only") and its dependent commit 94c296776403 ("i2c: muxes: pca954x:
> Reset if (de)select fails") because the first breaks all users of the
> driver, by requiring a completely optional reset-gpio driver.  These
> commits cause that mux driver simply stops working when optional
> reset-gpio is not included, but that reset-gpio is not pulled anyhow.
> 
> Driver cannot remove legacy reset-gpios handling.
> 
> Fixes: 690de2902dca ("i2c: muxes: pca954x: Use reset controller only")
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
> ---


Maybe I should also add to emphasize:

That offending commit 690de2902dca breaks the ABI which was:
1. documented at
Documentation/devicetree/bindings/i2c/i2c-mux-pca954x.yaml (line 57)
2. implemented in Linux kernel around v3.14.

This ABI breakage was not justified at all, not explained not even
mentioned in the commit msg, which is a requirement (see writing
bindings document).

Best regards,
Krzysztof