From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 42D621DD877; Tue, 28 Apr 2026 08:40:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777365655; cv=none; b=JBEcCBpOPdP8l5mml43fRhR1+7EB6i/t/km13WZ3/KCH8IqXxRbuSjeLoheZGh7rCgZ+yRQ7q7iyX7gC056fQKaJr67FKsgj71MVuGI1WcGbpsa5XIul8T94jrxeK/2kbDiTWFs45ShaRzK1/Eu0NaOzNoFQUt7jA0KkvZ7e8bI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777365655; c=relaxed/simple; bh=ItVJ5F6UDc9yJQwS4bk61nzLdZyax39MtPrAql5QAmA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=f1dJbb9Ksam16NaBm+mYTznMBLH7MehT6wmoIuLD4wkYiabLrfsaz+S2TIpQKYJbzcscXxK1K2m4JzKLk15eoGuXjzxk0iANGrGyyBs/cb2CBgKzjl4seEb8yTADr6JuC/APOxa15zNHYtUSHzyGu3cEm01CXk3XfD/UlUM87Yw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=cCgTwAd5; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="cCgTwAd5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 79B83C2BCB5; Tue, 28 Apr 2026 08:40:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777365654; bh=ItVJ5F6UDc9yJQwS4bk61nzLdZyax39MtPrAql5QAmA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=cCgTwAd5SRAVCZExSUQ051DjhblKL34IeBbpL1emWrxSkKmybKl7kXD47E/RnKMsh nfig+sNUR13rAgJu5kCdM8QdsR+TJ7w1X0kKHKeDPKi1x+5xViWO2mgNMMe83nHVxl sXM14/iy0v/n7q5gbMl0vIHQyX4NG/53LoGTQuTdQd6U0ztIDflr+Eq0TVeDaViR04 jJWsGJpU5XP1jQ8vicNeppu2MZufodPMba5Tl+DmPZ5OIVp1RJtuqLusw/iKITjo8I WHZo3e7X82JBTNQ5+kNAWaa8ZXihnfUuatrOOaM/dnv13GiO6upuNkfSFRvT40m3AG 3SCoKbo8siDNg== Message-ID: <006bd158-87aa-4fda-93cf-91f714fb72b6@kernel.org> Date: Tue, 28 Apr 2026 10:40:50 +0200 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: [PATCH v1 1/2] dt-bindings: gpio: fairchild,74hc595: add registers-default property To: Chanhong Jung Cc: Linus Walleij , Bartosz Golaszewski , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Maxime Ripard , linux-gpio@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org References: <33d515f13769c685e6811463a14e111252a7c58d.1776872453.git.happycpu@gmail.com> <20260423-quantum-precious-mantis-2481d7@quoll> <20260423103347.4054425-1-happycpu@gmail.com> From: Krzysztof Kozlowski Content-Language: en-US Autocrypt: addr=krzk@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 23/04/2026 12:33, Chanhong Jung wrote: > Hi Krzysztof, > > Thanks for the review. > >> You can fix the driver not to do that. Or fix the driver to properly >> parse hogs. I don't understand why exactly this one driver needs >> default registers stored in DT, but all other drivers in the kernel >> don't. > > I thought about both, but I don't think either works for this chip. > > 74HC595/74LVC594 is pure write-only: no MISO path, no register > read-back, and the data sheet defines the power-on state of the > parallel outputs as whatever /SRCLR and /OE do before the SPI master > is up. That's different from MCP23xxx, PCA953x, STMPE and the rest, > which are either readable (so the driver can RMW) or have a defined > reset value. None of those drivers need a seed property. This one > does, because there is nothing to read back and no defined state to > fall back on. > > Partial updates aren't possible either. set_value() has to shift the > full chain every time - see __gen_74x164_write_config() - so whatever This should also be explained in the commit msg. Best regards, Krzysztof