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 X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,UNPARSEABLE_RELAY autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B33F8C10F14 for ; Tue, 16 Apr 2019 08:42:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 865BD206BA for ; Tue, 16 Apr 2019 08:42:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728369AbfDPImf (ORCPT ); Tue, 16 Apr 2019 04:42:35 -0400 Received: from bhuna.collabora.co.uk ([46.235.227.227]:48842 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726857AbfDPImf (ORCPT ); Tue, 16 Apr 2019 04:42:35 -0400 Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: eballetbo) with ESMTPSA id 3AB10260FF2 Subject: Re: [RESEND PATCH v3 1/2] power: supply: add input voltage limit property To: Pavel Machek Cc: linux-pm@vger.kernel.org, sre@kernel.org, Sameer Nanda , bleung@chromium.org, rjw@rjwysocki.net, gwendal@chromium.org, linux-kernel@vger.kernel.org, Len Brown , groeck@chromium.org, Adam.Thomson.Opensource@diasemi.com, kernel@collabora.com References: <20190415220049.14924-1-enric.balletbo@collabora.com> <20190416071941.GB14538@amd> From: Enric Balletbo i Serra Message-ID: <8d1f70a7-46d6-f278-f58c-6a7e7a644d46@collabora.com> Date: Tue, 16 Apr 2019 10:42:30 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190416071941.GB14538@amd> Content-Type: text/plain; charset=windows-1252 Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Pavel, On 16/4/19 9:19, Pavel Machek wrote: > Hi! > >> This patch exposes a new property, similar to input current limit, to >> re-configure the maximum voltage from the external supply at runtime >> based on system-level knowledge or user input. > > Well, and I suspect it should expose input power limit, not input > voltage limit. > Oh, ok, I thought we were agree that input voltage had sense after had some discussion in v3. Seems that no, let me try to give you another example... > DC-DC convertor efficiency normally does not much depend on input > voltage.... > > Pavel > As we said we have a heat "problem" due the internal voltage conversions. Lets assume you have a linear regulator instead with a Vin range from 5V to 9V and we want an output of 3.3V/1A For 9V: Input power : P(in) = 9V x 1A = 9W Output power: P(out) = 3.3V x 1A = 3.3W Regulator power dissipated: P(reg) = P(in) - P(out) = 9W - 3.3W = 5.7W For 5V: Input power : P(in) = 5V x 1A = 5W Output power: P(out) = 3.3V x 1A = 3.3W Regulator power dissipated: P(reg) = P(in) - P(out) = 5W - 3.3W = 1,7W In the first case the regulator needs to dissipate more power, hence the temperature is greater than the second case. Thanks, Enric