From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 56DAEC433F5 for ; Fri, 10 Dec 2021 21:11:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243406AbhLJVP1 (ORCPT ); Fri, 10 Dec 2021 16:15:27 -0500 Received: from sin.source.kernel.org ([145.40.73.55]:56214 "EHLO sin.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243257AbhLJVP0 (ORCPT ); Fri, 10 Dec 2021 16:15:26 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sin.source.kernel.org (Postfix) with ESMTPS id 5106ACE2D3E; Fri, 10 Dec 2021 21:11:49 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 09AC3C00446; Fri, 10 Dec 2021 21:11:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1639170707; bh=ehvkwSBzHebalBRfzUXM/eqWv9XlwQOJTFk2risiuEE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=sIQZ5/gEbAn+zUpjcHSkFy+JKmxCIFY0DiXKcVGDGvgmpL4vPhx0pWsjIQUh0SY8k XWmzxMxPkYeSoUybJHis6k1wM7ubHJQMS38fduK4sggs7YC/JAsa54tEBFN2vk9jzn syv1e+75/NlIYS3rB0v4Bd4lifdAgKJexb/QtlKqgD5HM2sL/VnZXkdfyxl6QWlzhw /d5fW9vbqVSUF7O44AO3rMkbX9fh5m9dk5VNquV0e8kD2vJkvjNhDXGvPbFzPbxj31 2Apwjj93B6CSgXuNC6tfLzeMPHbvQa5Boz4DcxXctzH9knSL+RhGbxx7KCSD8+UMf1 bVI71x//VOTGw== Date: Fri, 10 Dec 2021 21:11:41 +0000 From: Mark Brown To: David Collins Cc: "Satya Priya Kakitapalli (Temp)" , Bjorn Andersson , Rob Herring , Liam Girdwood , swboyd@chromium.org, subbaram@codeaurora.org, Das Srinagesh , linux-arm-msm@vger.kernel.org, Lee Jones , devicetree@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH V4 1/6] dt-bindings: regulator: Add "regulator-min-dropout-voltage-microvolt" Message-ID: References: <1637314953-4215-1-git-send-email-quic_c_skakit@quicinc.com> <1637314953-4215-2-git-send-email-quic_c_skakit@quicinc.com> <6a44cb99-6894-c9ce-4f1e-5dee0939598c@quicinc.com> <23a47965-4ea9-5f6c-7e3c-27f5bd35f5b7@quicinc.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="aY21D3MOZ+5AaGhF" Content-Disposition: inline In-Reply-To: <23a47965-4ea9-5f6c-7e3c-27f5bd35f5b7@quicinc.com> X-Cookie: One picture is worth 128K words. Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --aY21D3MOZ+5AaGhF Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Wed, Dec 08, 2021 at 04:56:48PM -0800, David Collins wrote: > On 12/7/21 7:19 AM, Mark Brown wrote: > > On Tue, Dec 07, 2021 at 08:36:11PM +0530, Satya Priya Kakitapalli (Temp) wrote: > > that regulator. We absolutely can and do expect this to be board > > independent, it's a function of the design of the regulator. Sharing > > the input supply has no impact on this, the input voltage that the > > regulator needs just get fed into the requiremnts on the supply voltage. > The PM8008 LDOs are low noise LDOs intended to supply noise sensitive > camera sensor hardware. They can maintain output regulation with a > fixed headroom voltage. However, in order to guarantee high PSRR, the > headroom voltage must be scaled according to the peak load expected from > the each LDO on a given board. Thus, we included support for a DT > property to specify the headroom per LDO to meet noise requirements > across boards. Interesting... how much extra headroom are we talking about here? I'd be unsurprised to see this usually just quoted as part of the standard headroom requirement and this smells like the sort of thing that's going to be frequently misused. If the gains are something worth writing home about I'd think we should consider if it's better to support this dynamically at runtime based on load information and provide options for configuring the peak load information through DT instead for static configurations. That would fit in with the stuff we have for managing modes on DCDCs (which isn't really deployed but is there) and the API we have for allowing client drivers to indicate their load requirements at runtime that fits in with that. That'd allow us to only boost the headroom when it's really needed. --aY21D3MOZ+5AaGhF Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAABCgAdFiEEreZoqmdXGLWf4p/qJNaLcl1Uh9AFAmGzwo0ACgkQJNaLcl1U h9D5JAf/UH1JxBePimL0+Pp8KDDhkWrq3f8g7S6s1mh2CgcxSnjDVAhmWiFYh22A CdS7eEDRRbw9pDfERbScBSjw2NCFKRerD46BS+G/voolysHPatVwe6U/XmayvbJ6 A8Qkj07rDum73b1g1TmrYA+59rYMgtEFke5167sCmqhfo2XjldWcj89kAmr6+3ej YKmkEn5j9ulNqSskq49pY5QdSRAGxnaziUfuLjnbHwuTFQ3Ce59hdYJcmqny8CJp gP5pFW4q5Kj4vXHsP+d/Y16qnheo/jaxN4t4z+e8dF+Fdbtg9NIAV58BbsUurGab QZHp2ThzZotfK5DdkG17CEvYx5OnDg== =3Eej -----END PGP SIGNATURE----- --aY21D3MOZ+5AaGhF--