Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753214AbcKIRnj (ORCPT ); Wed, 9 Nov 2016 12:43:39 -0500 Received: from foss.arm.com ([217.140.101.70]:60088 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751420AbcKIRnh (ORCPT ); Wed, 9 Nov 2016 12:43:37 -0500 From: Sudeep Holla To: linux-pm@vger.kernel.org, "Rafael J . Wysocki" Cc: Sudeep Holla , linux-kernel@vger.kernel.org, Daniel Lezcano , Lorenzo Pieralisi , Andy Gross , Vincent Guittot Subject: [PATCH] drivers: cpuidle: assign enter_freeze to same as enter callback function Date: Wed, 9 Nov 2016 17:43:30 +0000 Message-Id: <1478713410-10727-1-git-send-email-sudeep.holla@arm.com> X-Mailer: git-send-email 2.7.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2224 Lines: 53 enter_freeze() callback is expected atleast to do the same as enter() but it has to guarantee that interrupts aren't enabled at any point in its execution, as the tick is frozen. CPUs execute ->enter_freeze with the local tick or entire timekeeping suspended, so it must not re-enable interrupts at any point (even temporarily) or attempt to change states of clock event devices. It will be called when the system goes to suspend-to-idle and will reduce power usage because CPUs won't be awaken for unnecessary IRQs (i.e. woken up only on IRQs from "wakeup sources") Since for all the states that have CPUIDLE_FLAG_TIMER_STOP flag set, local tick is stopped, we can reuse the same code for both the enter() and enter_freeze() callbacks. Only "coupled" cpuidle mechanism enables interrupts and doing that with timekeeping suspended is generally not safe. Since this generic DT based idle driver doesn't support "coupled" states, it is safe to assume that the interrupts are not re-enabled. This patch assign enter_freeze to same as enter callback function which helps to save power without any intermittent spurious wakeups from suspend-to-idle. Signed-off-by: Sudeep Holla --- drivers/cpuidle/dt_idle_states.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/drivers/cpuidle/dt_idle_states.c b/drivers/cpuidle/dt_idle_states.c index a5c111b67f37..5a087d108475 100644 --- a/drivers/cpuidle/dt_idle_states.c +++ b/drivers/cpuidle/dt_idle_states.c @@ -79,8 +79,17 @@ static int init_state_node(struct cpuidle_state *idle_state, desc = state_node->name; idle_state->flags = 0; - if (of_property_read_bool(state_node, "local-timer-stop")) + if (of_property_read_bool(state_node, "local-timer-stop")) { idle_state->flags |= CPUIDLE_FLAG_TIMER_STOP; + /* + * CPUIDLE_FLAG_TIMER_STOP guarantees that the local tick is + * stopped and since this is not a "coupled" state interrupts + * won't be enabled when it exits allowing the tick to be + * frozen safely. So enter() can be also enter_freeze() + * callback. + */ + idle_state->enter_freeze = match_id->data; + } /* * TODO: * replace with kstrdup and pointer assignment when name -- 2.7.4