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 3CBA3C433EF for ; Thu, 9 Dec 2021 00:56:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241654AbhLIBA2 (ORCPT ); Wed, 8 Dec 2021 20:00:28 -0500 Received: from alexa-out-sd-02.qualcomm.com ([199.106.114.39]:60807 "EHLO alexa-out-sd-02.qualcomm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241653AbhLIBA2 (ORCPT ); Wed, 8 Dec 2021 20:00:28 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=quicinc.com; i=@quicinc.com; q=dns/txt; s=qcdkim; t=1639011416; x=1670547416; h=subject:to:cc:references:from:message-id:date: mime-version:in-reply-to:content-transfer-encoding; bh=FX9/wHW1UB7swkH9l1Uv95qLCO4JveIAMi+icxTjyrs=; b=tBbGxJDkbsOsTwaFDD6e86YD0/Cu3xGUCZKbEvzGdy97FbyglL6rPtxx 3aoIGqEo5VL9ZtPF3dMSmCT1eRIkiwGw8O6jfdUFWQTO3LmLkE8jriDe1 v6RuGUZF5t3aAgm9VJOQn38m6hliJyphBO4kSczHnfRxhwcPvFhlJnrW9 s=; Received: from unknown (HELO ironmsg-SD-alpha.qualcomm.com) ([10.53.140.30]) by alexa-out-sd-02.qualcomm.com with ESMTP; 08 Dec 2021 16:56:55 -0800 X-QCInternal: smtphost Received: from nasanex01b.na.qualcomm.com ([10.46.141.250]) by ironmsg-SD-alpha.qualcomm.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Dec 2021 16:56:55 -0800 Received: from [10.46.160.247] (10.80.80.8) by nasanex01b.na.qualcomm.com (10.46.141.250) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.922.19; Wed, 8 Dec 2021 16:56:50 -0800 Subject: Re: [PATCH V4 1/6] dt-bindings: regulator: Add "regulator-min-dropout-voltage-microvolt" To: Mark Brown , "Satya Priya Kakitapalli (Temp)" CC: Bjorn Andersson , Rob Herring , Liam Girdwood , , , Das Srinagesh , , Lee Jones , , 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> From: David Collins Message-ID: <23a47965-4ea9-5f6c-7e3c-27f5bd35f5b7@quicinc.com> Date: Wed, 8 Dec 2021 16:56:48 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="windows-1252" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.80.80.8] X-ClientProxiedBy: nasanex01a.na.qualcomm.com (10.52.223.231) To nasanex01b.na.qualcomm.com (10.46.141.250) Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org 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: >> On 12/6/2021 11:55 PM, Mark Brown wrote: >>> On Mon, Dec 06, 2021 at 06:33:26PM +0530, Satya Priya Kakitapalli (Temp) wrote: > >>>> The min-dropout value (headroom) varies with boards, that's why we have a DT >>>> property for it. We overwrite the default value in driver with actual value >>>> read from DT > >>> Interesting. How exactly does that end up happening - presumably other >>> systems are going to run into it? > >> The parent supplies such as "vdd-l1-l2" are coming from other pmic >> regulators, which are shared supplies with other subsystems like BT, Display >> etc, they vary between boards as per requirements, so we cannot expect these >> to be fixed and so are the headroom values. We get the headroom values from >> PMIC systems team for every target. > > I don't think you're talking about the thing the code is saying it's > describing here. The regulator API is referring to the minimum droput > voltage that individual regulators require, that is how much higher the > input to a single regulator must be than the voltage being output by > 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. > > If there is a board specific constraint on the minimum voltage that a > given supply can have then that should be expressed using the normal > constraint mechanism, that's nothing to do with the headroom that the > regulators require to operate though. 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. As a minor note the PM8008 chip package has a single pin to supply LDOs 1 and 2 along with a single pin for LDOs 3 and 4. That is why vdd_l1_l2-supply is specified instead of vdd_l1-supply and vdd_l2-supply. Take care, David