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 A0FF2C433FE for ; Mon, 3 Jan 2022 14:37:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235632AbiACOh4 (ORCPT ); Mon, 3 Jan 2022 09:37:56 -0500 Received: from alexa-out-sd-01.qualcomm.com ([199.106.114.38]:51769 "EHLO alexa-out-sd-01.qualcomm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235213AbiACOfy (ORCPT ); Mon, 3 Jan 2022 09:35:54 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=quicinc.com; i=@quicinc.com; q=dns/txt; s=qcdkim; t=1641220554; x=1672756554; h=subject:to:cc:references:from:message-id:date: mime-version:in-reply-to:content-transfer-encoding; bh=Kkn0XEM2sZCVDqxZ85uch+XeIVY/Ku5AixlF8FXOOyo=; b=Br/3wSIyEYJXGQ3sw0GBE57ghvq2wU/RPC4qifGOPSlnCkFoOi2Tqrk+ Y8GltsshTfPbmRRhN+2/QKtq1EQ3oN9APzNf6mORb6V8fVXe+lziz0wEu 2iuJk8qSXHDJG9DX3l9UHEMtPuBJVlnipor3q8P5BfDRwEzR2t01RlEu5 E=; Received: from unknown (HELO ironmsg01-sd.qualcomm.com) ([10.53.140.141]) by alexa-out-sd-01.qualcomm.com with ESMTP; 03 Jan 2022 06:35:53 -0800 X-QCInternal: smtphost Received: from nasanex01c.na.qualcomm.com ([10.47.97.222]) by ironmsg01-sd.qualcomm.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Jan 2022 06:35:51 -0800 Received: from nalasex01a.na.qualcomm.com (10.47.209.196) by nasanex01c.na.qualcomm.com (10.47.97.222) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.922.19; Mon, 3 Jan 2022 06:35:51 -0800 Received: from [10.216.7.79] (10.80.80.8) by nalasex01a.na.qualcomm.com (10.47.209.196) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.922.19; Mon, 3 Jan 2022 06:35:45 -0800 Subject: Re: [PATCH V4 1/6] dt-bindings: regulator: Add "regulator-min-dropout-voltage-microvolt" To: Mark Brown , David Collins 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> <23a47965-4ea9-5f6c-7e3c-27f5bd35f5b7@quicinc.com> From: "Satya Priya Kakitapalli (Temp)" Message-ID: <012a0a96-ab0e-e844-12e1-f2272bf2506d@quicinc.com> Date: Mon, 3 Jan 2022 20:05:40 +0530 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Originating-IP: [10.80.80.8] X-ClientProxiedBy: nasanex01a.na.qualcomm.com (10.52.223.231) To nalasex01a.na.qualcomm.com (10.47.209.196) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/11/2021 2:41 AM, Mark Brown wrote: > 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. This means Dynamic headroom control feature needs to be implemented. I need to explore more on this and gather info from team, Could we merge the present driver with "static headroom" for now? I'll do a follow up series to implement this feature.