Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757112Ab3HLQoR (ORCPT ); Mon, 12 Aug 2013 12:44:17 -0400 Received: from mail-ee0-f54.google.com ([74.125.83.54]:39536 "EHLO mail-ee0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756343Ab3HLQoQ (ORCPT ); Mon, 12 Aug 2013 12:44:16 -0400 Message-ID: <520910DA.4000203@gmail.com> Date: Mon, 12 Aug 2013 18:44:10 +0200 From: Sebastian Hesselbarth User-Agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/17.0 Thunderbird/17.0 MIME-Version: 1.0 To: Ezequiel Garcia CC: Russell King , Lior Amsalem , Thomas Petazzoni , Jason Cooper , Andrew Lunn , linux-kernel@vger.kernel.org, Gregory Clement , linux-arm-kernel@lists.infradead.org, Alexander Shiyan , Linus Walleij Subject: Re: [PATCH 1/3] ARM: Introduce atomic MMIO clear/set References: <1376138582-7550-1-git-send-email-ezequiel.garcia@free-electrons.com> <20130810140237.GB3080@localhost> <20130810140927.GC3080@localhost> <1376149388.716003514@f150.i.mail.ru> <20130810155552.GB17936@localhost> <20130812154646.GA5460@localhost> In-Reply-To: <20130812154646.GA5460@localhost> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1894 Lines: 45 On 08/12/13 17:46, Ezequiel Garcia wrote: >> Indeed, syscon looks like a nice match for this use case. >> (although it still looks like an overkill to me). >> >> I've been trying to implement a working solution based in syscon but I'm >> unable to overcome an issue. >> >> The problem is that we need the register/regmap to initialize the clocksource >> driver for this machine (aka the timer). Of course, this happens at a >> *very* early point, way before the syscon driver is available... :-( >> >> Maybe someone has an idea? > > Sebastian, Russell: I can't find the previous mail where you proposed > this solution to address the shared register issue between Kirkwood's > watchdog and clocksource. Russell first mentioned an atomic modify function here: http://archive.arm.linux.org.uk/lurker/message/20130618.113606.d7d4fe4b.en.html Linus Walleij already suggested mfd/syscon as a container for protected register accesses later. > Is this what you had in mind? The pro of a generic atomic clear/set is that we can use it very early, on all platforms, and from totally unrelated drivers. As you already mentioned, using syscon from timers will get us into into trouble, because it has not been registered. > Do you think trying to use a regmap could be better (given we can > sort out the problem explained above)? Given the small number of registers we need to protect and especially for using it in timers, I'd prefer your proposal. Otherwise, I guess, we would have to mimic mfd/syscon for time-orion and time-armada-370-xp and make wdt-orion depend on it. I doubt we can make any use of mfd/syscon for the timer use case. Sebastian -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/