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 5E9A91DD543; Mon, 29 Sep 2025 14:31:33 +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=1759156294; cv=none; b=C3TwVRyJgwxMlFHzahc3NO3DPE1DBCH9zhO/whpeSw0XxKEzE/1bitNigQpBgukinygeevNvaPm+OtToXO7EJSAn0ALRvE5XNVMUH5nMiKFO8N8mS5bRBNaKOX38ge2z2oDghZ/g+zWgkh6Yp/kUwO1QzLwDgjN4nApZSq6XWC4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759156294; c=relaxed/simple; bh=sKuqKNpE5dhMtZf1zaC2ZqjURpyd3C7l8Ef/qH3un8E=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Y/WpLQQAY2VhIgq05GZw/Y5gWPTcD50VG9tKgVWCj9VSMe47LRQ4pPcHW7qa+Ymgbzt0AeqeqnysAAevuinVnpYfLSO5ovUaLudG3N+dsCkGTdx4yLYa4b58I73iZgL6lduSgbMgnROmvHM62Am3hddILF/UFsJMpIwp4REagP8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Ybofpbcx; 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="Ybofpbcx" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 68AE4C4CEF4; Mon, 29 Sep 2025 14:31:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1759156293; bh=sKuqKNpE5dhMtZf1zaC2ZqjURpyd3C7l8Ef/qH3un8E=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Ybofpbcx+ejkNvAv75607kTZIE8CUsY9qhrXc/yrJ9X2bu9eV4OnGXQ3TNrOD/y2P ZTx2iK+hamBmIKKHDaVWhoOTCftImvcznOCK+7AEffOegIkND9rMYBhjXJdQX1r1ZL 0JZPrZuBsBi3OkjiTPDsLn7YSdXtt3i13qbb2sqBLpmyWZ+oVdhkzjg1wkMuDpihUy 6H4hKACxj53QRJs6VTVZG6utz4nyFWuKrwYhNjvjyPwNTkosbGPUWq/6n6pcvlANgh fQ2kDFeXinDxHted7Q2+zz5VDaq8aUMue0z6xZZqc8r3t6Teq5PIR23t0f4AHQZWzI MmqWDPc+OcTRw== Date: Mon, 29 Sep 2025 09:31:32 -0500 From: Rob Herring To: Jonathan Cameron Cc: Marcelo Schmitt , linux-iio@vger.kernel.org, devicetree@vger.kernel.org, linux-doc@vger.kernel.org, linux-spi@vger.kernel.org, linux-kernel@vger.kernel.org, michael.hennerich@analog.com, nuno.sa@analog.com, eblanc@baylibre.com, dlechner@baylibre.com, andy@kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org, corbet@lwn.net, marcelo.schmitt1@gmail.com, Linus Walleij , Bartosz Golaszewski , linux-gpio@vger.kernel.org Subject: Re: [PATCH v3 7/8] dt-bindings: iio: adc: adi,ad4030: Add ADAQ4216 and ADAQ4224 Message-ID: <20250929143132.GA4099970-robh@kernel.org> References: <5dc08b622dac1db561f26034c93910ccff75e965.1758916484.git.marcelo.schmitt@analog.com> <20250928111955.175680cb@jic23-huawei> Precedence: bulk X-Mailing-List: linux-spi@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: <20250928111955.175680cb@jic23-huawei> On Sun, Sep 28, 2025 at 11:19:55AM +0100, Jonathan Cameron wrote: > On Fri, 26 Sep 2025 17:40:47 -0300 > Marcelo Schmitt wrote: > > > ADAQ4216 and ADAQ4224 are similar to AD4030 except that ADAQ devices have a > > PGA (programmable gain amplifier) that scales the input signal prior to it > > reaching the ADC inputs. The PGA is controlled through a couple of pins (A0 > > and A1) that set one of four possible signal gain configurations. > > > > Signed-off-by: Marcelo Schmitt > > --- > > Change log v2 -> v3 > > - PGA gain now described in decibels. > > > > The PGA gain is not going to fit well as a channel property because it may > > affect more than one channel as in AD7191. > > https://www.analog.com/media/en/technical-documentation/data-sheets/AD7191.pdf > > > > I consulted a very trustworthy source [1, 2] and learned that describing signal > > gains in decibels is a common practice. I now think it would be ideal to describe > > these PGA and PGA-like gains with properties in decibel units and this patch > > is an attempt of doing so. The only problem with this approach is that we end up > > with negative values when the gain is lower than 1 (the signal is attenuated) > > and device tree specification doesn't support signed integer types. As the > > docs being proposed fail dt_binding_check, I guess I have to nack the patch myself. > > Any chance of dt specification eventually support signed integers? > > Any suggestions appreciated. > > > > [1] https://en.wikipedia.org/wiki/Decibel > > [2] https://en.wikipedia.org/wiki/Gain_(electronics) > > I still wonder if the better way to describe this is to ignore that it > has anything to do with PGA as such and instead describe the pin strapping. > > DT folk, is there an existing way to do that? My grep skills are failing to > spot one. > > We've papered over this for a long time in various IIO drivers by controlling > directly what the pin strap controls with weird and wonderful device specific > bindings. I wonder if we can't have a gpio driver + binding that rejects all > config and just lets us check the current state of an output pin. Kind of a > fixed mode regulator equivalent for gpios. If these are connected to GPIOs, isn't it possible that someone will want to change their value? Other than some generic 'pinstrap-gpios' property, I don't see what we'd do here? I don't feel like pin strapping GPIOs is something that we see all that often. Rob