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 AACEE258EF9; Wed, 6 May 2026 01:43:24 +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=1778031804; cv=none; b=eGDgXTeK0k/fagyTjxKau96VQy2KZ4aLinIS5NLSD9fYL3+CTDRZmtv4OrcZ+/zkL8uO3eONmwa4/UC+vCB1hLRBwpsR5Ftk0ZmqnRfgGP2WJLo8kzyEs2legNFdY0C17bvcXAzt2TfNPN4LxsXoOtsUVPr8lu5/Kzk+cskGpnM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778031804; c=relaxed/simple; bh=vSPiDgJ0IkynnZonv8Pb+B5VUe/T3NmI2G4+fg17vlk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=m/X4W0lwS8XgE/5lOWci1yhW5gz4C8Nf+zpZvv8SAH1zBBjg0syHpH8JVo9erxFS4fpA+fZrTLq+iCVYpjjnDJ1519NFgX++AANInE9Z7N/rHRWLz7/ES47wEw8a03ipULTRxrPq2efjelgw72YyHd2VvS8G3phzAASpAKLk9Fw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=YIWF5+nQ; 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="YIWF5+nQ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 11332C2BCB4; Wed, 6 May 2026 01:43:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778031804; bh=vSPiDgJ0IkynnZonv8Pb+B5VUe/T3NmI2G4+fg17vlk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=YIWF5+nQEZRPqEYYEOo13NiSq/4G3uObvMlisFqsvSk4sg+Z7wZ+Vhlj0cf9eviBZ H/aV1zvXqD6NDraiftci1LHUasqpW8hzynBgRP0x6eKvV7alJz1oJfm+LRPxHcR5pZ MTawc7sRQIFFfbZOlUU8PIpG0TEdSgNCqYsngbHH+7Hp1HgUtWcwx1ZAr3cZPXR+2H +AQUDEbcqMcJsU8VYWHlPKh4AAus7Nc8U2X01yFwjdKtLIMR+RODA3lfebIDD3d1yi 1INYC5M8AbCOHv/2+b2PjR1zxjlt2xe+JNin3piGraOgKYkAC4PLmfiZINe4zg37EH 6P+QjfgasM5vA== Date: Tue, 5 May 2026 20:43:21 -0500 From: "Rob Herring (Arm)" To: Chanhong Jung Cc: Bartosz Golaszewski , linux-kernel@vger.kernel.org, linux-gpio@vger.kernel.org, devicetree@vger.kernel.org, Linus Walleij , Conor Dooley , Krzysztof Kozlowski , Maxime Ripard Subject: Re: [PATCH v2 1/2] dt-bindings: gpio: fairchild,74hc595: add lines-initial-states property Message-ID: <177803180135.280005.13996377729144610896.robh@kernel.org> References: <20260429035134.1023330-2-happycpu@gmail.com> Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260429035134.1023330-2-happycpu@gmail.com> On Wed, 29 Apr 2026 12:51:33 +0900, Chanhong Jung wrote: > The 74HC595 and 74LVC594 shift registers latch their outputs until the > first serial write, so boards that depend on a specific power-on pattern > (for example active-low indicators, reset lines, or other signals that > must come up non-zero) have no way to express that today: the Linux > driver always writes zeros from its zero-initialised buffer during > probe. > > Document support for the existing lines-initial-states bitmask, already > defined for nxp,pcf8575, so the same convention covers this output-only > device. Bit N corresponds to GPIO line N. Because the 74HC595/74LVC594 > family is push-pull output only (no input mode, no high-impedance state > under software control), bit=0 drives the line low and bit=1 drives it > high; this differs from nxp,pcf8575, where the 0/1 polarity reflects the > quasi-bidirectional nature of that part. > > The bitmask covers up to 32 lines, which fits the typical 1-4 chip > cascades that appear in tree. Should longer chains require seeding in > the future, the property can be extended to a uint32-array without > breaking the bit-N-equals-line-N convention. > > Suggested-by: Linus Walleij > Signed-off-by: Chanhong Jung > --- > .../devicetree/bindings/gpio/fairchild,74hc595.yaml | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > Reviewed-by: Rob Herring (Arm)