Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755528Ab3C3L4j (ORCPT ); Sat, 30 Mar 2013 07:56:39 -0400 Received: from mail-ve0-f182.google.com ([209.85.128.182]:45473 "EHLO mail-ve0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754315Ab3C3L4h (ORCPT ); Sat, 30 Mar 2013 07:56:37 -0400 MIME-Version: 1.0 In-Reply-To: <20130330100408.GA17995@n2100.arm.linux.org.uk> References: <1364549049-29278-1-git-send-email-ning.n.jiang@gmail.com> <5155DE43.4000601@codeaurora.org> <20130330100408.GA17995@n2100.arm.linux.org.uk> Date: Sat, 30 Mar 2013 19:56:36 +0800 Message-ID: Subject: Re: [PATCH] ARM: timer: Shutdown clock event device when stopping local timer From: Ning Jiang To: Russell King - ARM Linux Cc: Stephen Boyd , kgene.kim@samsung.com, davidb@codeaurora.org, dwalker@fifo99.com, bryanh@codeaurora.org, john.stultz@linaro.org, tglx@linutronix.de, linus.walleij@linaro.org, shawn.guo@linaro.org, rob.herring@calxeda.com, arnd@arndb.de, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-samsung-soc@vger.kernel.org, linux-arm-msm@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2261 Lines: 49 2013/3/30 Russell King - ARM Linux : > On Sat, Mar 30, 2013 at 05:57:38PM +0800, Ning Jiang wrote: >> 2013/3/30 Stephen Boyd : >> > On 03/29/13 02:24, ning.n.jiang@gmail.com wrote: >> >> From: Ning Jiang >> >> >> >> Currently there are two problems when we try to stop local timer. >> >> First, it calls set_mode function directly so mode state is not >> >> updated for the clock event device. Second, it makes the device >> >> unused instead of shutdown. >> > >> > What device is this a problem on? I believe this only matters to drivers >> > which enable their timer in their set_next_event() callback? But even >> > then, does anything actually happen because the interrupt should have >> > been disabled in the local timer stop callback. >> > >> >> Right. Drivers which enable timer in set_next_event() will have this problem. >> It will not have functional problem in my case. But my device cannot enter >> low power mode with a pending interrupt even if it is disabled. > > You're not telling us what you have discovered. How does set_next_event() > get called after we've set the mode to UNUSED in the current code? In the current code we did not set the mode to UNUSED but only call set_mode callback function for the clock event device. This normally disables current clock event device. The dying CPU eventually will switch to idle thread, call tick_nohz_idle_enter(), try to cancel the sched_timer and reprogram the next event. Then set_next_event() gets called. The call stack will be like: tick_nohz_idle_enter -> __tick_nohz_idle_enter -> tick_nohz_stop_sched_tick -> hrtimer_cancel -> hrtimer_try_to_cancel -> remove_hrtimer -> __remove_hrtimer -> hrtimer_force_reprogram -> tick_program_event -> clockevents_program_event -> set_next_event In set_next_event() we'll re-enable and re-program the clock event device. -- 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/