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 33F8037168; Wed, 20 Dec 2023 13:59:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Yqgbtzax" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 179A0C433C8; Wed, 20 Dec 2023 13:59:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1703080767; bh=6nS84hjjQDBdt98iBZz8SZKjaQiY/+oGazVY2peowjk=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=YqgbtzaxiEfXtgf5evVK8bogkq9OsOhUYJ+l4TRwqelM/a2pd2qUwDkdEvmggUzVT C84OALMEEsi3He2Uub1S5SHNoEwk2X5tH0VuL1Jp78rBF55Gvh5HuIRjIOnH5zlUas 00Rhoq1V5JZ863fBtdOoIjpssYLwchUicLqbnFYsVu4FRb+nlvlt5ni/wDEHngkt7r oTU2E0B/+u8hK+00Wuh6JnOzrTNFVEdO2vHslfGEgZ4y5oUgguUT7JPL8luQy1gKhJ W+w3nIYhnaKnJoh4njAAZvm7Wa13iecMmcYzwCcYxP2Z3KxS8SYQvSJJQY0YsmlQEN wzHSH5WIUKhVg== Date: Wed, 20 Dec 2023 13:59:13 +0000 From: Jonathan Cameron To: Mike Looijmans Cc: Jonathan Cameron , Conor Dooley , devicetree@vger.kernel.org, linux-iio@vger.kernel.org, Conor Dooley , Krzysztof Kozlowski , Lars-Peter Clausen , Rob Herring , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] dt-bindings: iio: adc: ti-ads1298: Add driver Message-ID: <20231220135913.50edaa7f@jic23-huawei> In-Reply-To: References: <1b153bce-a66a-45ee-a5c6-963ea6fb1c82.949ef384-8293-46b8-903f-40a477c056ae.618139b3-8cb2-4e4c-9283-9e3787c70105@emailsignatures365.codetwo.com> <20231213094722.31547-1-mike.looijmans@topic.nl> <20231213-diffuser-disposal-ea21bbce8b64@spud> <20231214102244.000052a3@Huawei.com> X-Mailer: Claws Mail 4.2.0 (GTK 3.24.38; x86_64-pc-linux-gnu) 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-Transfer-Encoding: 7bit > >>> + avdd-supply: > >>> + description: > >>> + Analog power supply, voltage between AVDD and AVSS. When providing a > >>> + symmetric +/- 2.5V, the regulator should report 5V. > > > > Any precedence in tree for doing this? I thought we had bindings that required negative > > supplies to be specified separately if present - so this would need to be 2 > > supplies. e.g. > > https://elixir.bootlin.com/linux/v6.7-rc5/source/Documentation/devicetree/bindings/iio/adc/ti,adc12138.yaml#L37 > > > > Given that some serious thought... > > Splitting into positive and negative supplies would make sense if the chip > would have terminals for positive, negative and ground. Which it does not > have, there's only positive and negative (which the datasheet misleadingly > calls "analog ground"). > > The analog voltage supplied to the chip has no effect on its outputs, the > analog supply must be connected between the AVDD and AVSS pins. Its relation > to analog ground is not relevant, so whether the voltages are +5/0 or > +2.5/-2.5 or +4/-1 or whatever does not affect the output of the ADC, which > only reports the difference between its "p" and "n" input signals. It only > affects the range of the inputs, as it cannot measure (p or n) outside the > analog supply. > Ah. Not having seen any isolators, I assumed this device was running against a common ground with the digital side of things. AVSS to DGND is between -3 and 0.2 so I think there is a ground even if it's not directly connected. Given this only operates in differential mode the fact both signals are referenced to +-vref which is from VASS doesn't matter in the end and any offset goes away. So yes I think I agree. This should be a single supply. Jonathan