Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934438AbbDQObN (ORCPT ); Fri, 17 Apr 2015 10:31:13 -0400 Received: from foss.arm.com ([217.140.101.70]:40218 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754158AbbDQObI (ORCPT ); Fri, 17 Apr 2015 10:31:08 -0400 Date: Fri, 17 Apr 2015 15:08:19 +0100 From: Lorenzo Pieralisi To: Tomeu Vizoso Cc: "Rafael J. Wysocki" , "linux-tegra@vger.kernel.org" , "linux-pm@vger.kernel.org" , "Rafael J. Wysocki" , Russell King , Stephen Warren , Thierry Reding , Alexandre Courbot , Bartlomiej Zolnierkiewicz , Kyungmin Park , Daniel Lezcano , Kukjin Kim , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] ARM: tegra: cpuidle: implement cpuidle_state.enter_freeze() Message-ID: <20150417140819.GB2347@red-moon> References: <1428490480-10144-1-git-send-email-tomeu.vizoso@collabora.com> <20150408115546.GA24271@red-moon> <552643E1.3060200@collabora.com> <285738930.THBQOWvsah@vostro.rjw.lan> <20150410100844.GC23730@red-moon> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1724 Lines: 41 On Thu, Apr 16, 2015 at 03:37:19PM +0100, Tomeu Vizoso wrote: [...] > >> I don't know what FIQs are. :-) > > > > In short, fast IRQs, it is a separate IRQ line handled as a separate > > exception source with some private (banked) registers that minimize registers > > saving/restoring. They are not identical to NMI on x86, since > > their behaviour (handling) may be overriden by platforms and they > > can be masked. > > > >> ->enter_freeze is entered with interrupts disabled on the local CPU. It is > >> not supposed to re-enable them. That is, while in the ->enter_freeze callback > >> routine, the CPU must not be interrupted aby anything other than NMI. > > > > It boils down to what FIQs handlers are allowed to do with tick frozen > > and what they are (may be) currently used for. > > > > Russell has more insights on this than I do, in particular what FIQs are > > currently used for on ARM and if we can leave them enabled safely with tick > > frozen. > > But even if it's currently safe to leave them enabled, is there any > reason for not disabling them? Ok, the point here is: either it is safe, and you leave them enabled, or it is not and we must disable them *before* enter_freeze() is entered. Disabling them in the platform enter_freeze() hook does not make sense, because this means we run with FIQs enabled with tick frozen, either it is safe or it is not, it can't be both. I would ask Russell opinion on this, before making any decision. Lorenzo -- 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/