From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756021AbcHYEr3 (ORCPT ); Thu, 25 Aug 2016 00:47:29 -0400 Received: from mail-wm0-f68.google.com ([74.125.82.68]:33299 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755888AbcHYEr0 (ORCPT ); Thu, 25 Aug 2016 00:47:26 -0400 MIME-Version: 1.0 In-Reply-To: <5696A002.6050402@ti.com> References: <20160111202421.GA12777@atomide.com> <20160112000917.GC12777@atomide.com> <417BBA32-A7DC-40CD-8A6B-EA910B1C9C13@goldelico.com> <001346CD-CF31-4FEF-B406-B89EEBDFA063@goldelico.com> <56966558.1070608@ti.com> <569669C5.2070200@ti.com> <20160113164856.GF12777@atomide.com> <5696896F.4090309@ti.com> <20160113180006.GJ12777@atomide.com> <2B99611A-5D2E-4D17-A17D-0150516109FD@goldelico.com> <56969800.5010206@ti.com> <5696A002.6050402@ti.com> From: Matthijs van Duin Date: Thu, 25 Aug 2016 04:43:40 +0200 Message-ID: Subject: Re: [PATCH 1/3] ARM: dts: omap5-board-common: enable rtc and charging of backup battery To: Nishanth Menon Cc: "H. Nikolaus Schaller" , Tony Lindgren , Grygorii Strashko , Laxman Dewangan , =?UTF-8?Q?Beno=C3=AEt_Cousson?= , Rob Herring , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , Russell King , linux-omap , devicetree , LKML , Marek Belisko , =?UTF-8?Q?Gra=C5=BEvydas_Ignotas?= , Keerthy Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13 January 2016 at 19:18, Nishanth Menon wrote: > As you already see it is ridiculously round about way of protecting RTC > time.. but anyways, for what ever reason, that was mandatory function to > support on certain product lines. Having secure date/time is probably necessary for some digital rights management schemes; e.g. you rent a movie for limited time, but it may not always be acceptable to require working internet connectivity to be able to hit the play button hence the need to rely on a secure RTC. There wouldn't even be an SMC for setting the RTC, probably it would synchronize when the secure-world shizzle contacts the Big Server O'Secrety Bits. :P Protecting pinmux through the L4 firewall sounds hilarious: the whole ctrl_core module (0x4a002000 - 0x4a002fff) is a single firewall region. All permitted access to it by linux would have to be redirected to an SMC or similar. On 13 January 2016 at 20:05, Nishanth Menon wrote: > An internal feedback I got some time back on AM57 (not OMAP5) - context > was that we were discussing if an external pull up resistor was needed > for a GPIO button: > "Internal pull-ups are relatively weak (ranging to 100kOhm or higher) Unlike the OMAP5, AM57xx uses 1.8V/3.3V drivers for its generic IOs, which have to do magic to not get fried by such high voltages. Crappier specs result, especially for pulling up to 3.3V: 1.8V mode, pull-down current while pin is held high: 50-210 uA 3.3V mode, pull-down current while pin is held high: 40-200 uA 1.8V mode, pull-up current while pin is held low: 60-200 uA 3.3V mode, pull-up current while pin is held low: 10-290 uA Note the worst-case equivalent pull-up resistance in 3.3V mode is 330 kOhm, eleven times higher than in 1.8V mode. Matthijs