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=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_NEOMUTT 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 5FD3DC04AA9 for ; Thu, 2 May 2019 21:01:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2F4A22063F for ; Thu, 2 May 2019 21:01:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726324AbfEBVBm (ORCPT ); Thu, 2 May 2019 17:01:42 -0400 Received: from bhuna.collabora.co.uk ([46.235.227.227]:42512 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725962AbfEBVBm (ORCPT ); Thu, 2 May 2019 17:01:42 -0400 Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: sre) with ESMTPSA id 815DC2804F8 Received: by earth.universe (Postfix, from userid 1000) id C4E233C0D1B; Thu, 2 May 2019 23:01:38 +0200 (CEST) Date: Thu, 2 May 2019 23:01:38 +0200 From: Sebastian Reichel To: Enric Balletbo i Serra Cc: Pavel Machek , linux-pm@vger.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 Subject: Re: [RESEND PATCH v3 1/2] power: supply: add input voltage limit property Message-ID: <20190502210138.ekrjvg4jex5x2tbo@earth.universe> References: <20190415220049.14924-1-enric.balletbo@collabora.com> <20190416071941.GB14538@amd> <8d1f70a7-46d6-f278-f58c-6a7e7a644d46@collabora.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="vwdv5qwmkpp26lsd" Content-Disposition: inline In-Reply-To: <8d1f70a7-46d6-f278-f58c-6a7e7a644d46@collabora.com> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --vwdv5qwmkpp26lsd Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Hi, On Tue, Apr 16, 2019 at 10:42:30AM +0200, Enric Balletbo i Serra wrote: > On 16/4/19 9:19, Pavel Machek wrote: > >> 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. > >=20 > > Well, and I suspect it should expose input power limit, not input > > voltage limit. >=20 > Oh, ok, I thought we were agree that input voltage had sense after had so= me > discussion in v3. Seems that no, let me try to give you another example... >=20 > > DC-DC convertor efficiency normally does not much depend on input > > voltage.... >=20 > As we said we have a heat "problem" due the internal voltage conversions. >=20 > 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) =3D 9V x 1A =3D 9W > Output power: P(out) =3D 3.3V x 1A =3D 3.3W > Regulator power dissipated: P(reg) =3D P(in) - P(out) =3D 9W - 3.3W =3D = 5.7W >=20 > For 5V: > Input power : P(in) =3D 5V x 1A =3D 5W > Output power: P(out) =3D 3.3V x 1A =3D 3.3W > Regulator power dissipated: P(reg) =3D P(in) - P(out) =3D 5W - 3.3W =3D = 1,7W >=20 > In the first case the regulator needs to dissipate more power, hence the > temperature is greater than the second case. I would be surprised, if a linear regulator is being used in this place :) That would basically render functionality of higher voltage completley useless and a good reason to always limit to 5V. For the generic case I agree with Pavel, that control over the power (voltage * current) is the better choice. Still I believe it makes sense to have a control knob for the voltage available, since some hardware designs suck. For example the bad hardware design might be the remote side, that has issues providing some voltages and this would make it possible to debug that. -- Sebastian --vwdv5qwmkpp26lsd Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCgAdFiEE72YNB0Y/i3JqeVQT2O7X88g7+poFAlzLWq0ACgkQ2O7X88g7 +pqzKhAAk5VXBCW5KI1uBgScQTbWw/6eWgTGX9m/vUX5YVUhvRBfVg0h4l6HmOJl bbg71lCAGtp0xS0h9YPxuU1MrrLW/HlnbSdz69/WB6zPeKbYx3Wn4v/3M1UnbcCf HE0svSdJhyFY0Iyo7g3VMiJRjDesw1ceUoVHDSD092o/H4PECMuFFqqFnCes4j3X Fgaztk2H6EEpuJ7cmov/266hmL59SsDBx05O0Zk2ezVku1eoYh4BHS1stt3jMOZj xbTo7Meq0oIra6EpB1jdKh7DAkwRNkaChlLuXJdZZ6VkmULCQtQ6K91/mG3qg9rR MEbPJDGuzbB+zqYoCLVHEc7ykhgxiAuWoXTe9NB9rR9JfQATtworXuUg3M715/Id D52e7xbLMR1CGxPKeybUmg+oJE6dUDnGSwRHnTFOL222hmE5hvEXI8i0dNUV0dqQ s2aqeMaagd10jWmdDazKYGC6xGj616XqNABKwo0QzKaWprhhtF6qE5/EyBtywECX 4V3KoF3H9a/47hj9dXEy3BHsqHE4j9vfUuT5GxTHtDaEYiR+ZmOamixd6m3jrkL6 zc6dNZV5Sa1I39Ofi4F/Wu+ds2kP3Akm8HlvAzic4i7CjeYbcTuP9WuPvtZ5Lt/U x6zMXiOOMlghHzwmbrFkn9DRSot0Pk00QBFFU5F4HEm89utFRHE= =wEeJ -----END PGP SIGNATURE----- --vwdv5qwmkpp26lsd--