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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 3C4A5C43387 for ; Tue, 8 Jan 2019 18:47:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 111BB2070B for ; Tue, 8 Jan 2019 18:47:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729548AbfAHSrU (ORCPT ); Tue, 8 Jan 2019 13:47:20 -0500 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:59655 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729179AbfAHSrT (ORCPT ); Tue, 8 Jan 2019 13:47:19 -0500 Received: by atrey.karlin.mff.cuni.cz (Postfix, from userid 512) id E2CF1808F7; Tue, 8 Jan 2019 19:47:09 +0100 (CET) Date: Tue, 8 Jan 2019 19:47:14 +0100 From: Pavel Machek To: Enric Balletbo Serra Cc: Enric Balletbo i Serra , Linux PM list , Sebastian Reichel , Sameer Nanda , Benson Leung , Gwendal Grignou , linux-kernel , Guenter Roeck , Adam.Thomson.Opensource@diasemi.com, kernel@collabora.com, "Rafael J. Wysocki" , Len Brown Subject: Re: [PATCH v3 1/2] power: supply: add input voltage limit property Message-ID: <20190108184714.GA11289@amd> References: <20181213120944.30967-1-enric.balletbo@collabora.com> <20181213222000.GA12302@amd> <2fcfc863-3218-55e8-2a0f-75d7cb2d55db@collabora.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="GvXjxJ+pjyke8COw" Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --GvXjxJ+pjyke8COw Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Hi! > > >> For folks hacking on Pixel Cs (which is now outside of Google's offi= cial > > >> support window for Android) and customizing their own kernel and use= rspace > > >> this would be acceptable, but we wanted to expose this feature in the > > >> power supply properties because the feature does exist in the Emedded > > >> Controller firmware of the Pixel C and all of Google's Chromebooks w= ith > > >> USB-C made since 2015 in case someone running an up to date kernel w= anted > > >> to limit the charging power for thermal or other reasons. > > >> > > >> 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. > > > > > > Could we get power input limit, instead? > > > > > > > I'm open but I have some concerns, so lets discuss a bit about it :) > > > > According to the USB PD 2.0 specs if we limit the source at 15W we can = get 5V/3A > > or 9V/1.67A, if I am not mistaken the higher voltage caused problem sin= ce the > > conversion to lower internal voltages generated more heat, so in this c= ase > > 9V/1.67A is not a valid value for us (maybe someone from ChromeOS can c= onfirm > > this?). > Around Xmas are bad dates to start a discussion. I don't want this > patch will be forgotten, so a gentle ping on your thoughts on this :) > (just in case) If someone can indeed confirm it is _voltage_ that is problematic, then approach is ok with me. [But I'd not expect buck convertor efficiency to differ greatly based on input voltage.] Best regards, Pavel =09 > > >> +What: /sys/class/power_supply//input_vol= tage_limit > > >> +Date: Nov 2018 > > >> +Contact: linux-pm@vger.kernel.org > > >> +Description: > > >> + This entry configures the incoming VBUS voltage limit c= urrently > > >> + set in the supply. Normally this is configured based on > > >> + system-level knowledge or user input (e.g. This is part= of the > > >> + Pixel C's thermal management strategy to effectively li= mit the > > >> + input power to 5V when the screen is on to meet Google'= s skin > > >> + temperature targets). Note that this feature should not= be > > >> + used for safety critical things. --=20 (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blo= g.html --GvXjxJ+pjyke8COw Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iEYEARECAAYFAlw08DIACgkQMOfwapXb+vKW6wCghA+1ikUGqjLf99j1wZRH6Iac OB0AnROGmZU1+WiqOg7Bmk/EoWE3hSkk =2G+L -----END PGP SIGNATURE----- --GvXjxJ+pjyke8COw--