From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tony Lindgren Subject: [PATCH 7/9] ARM: OMAP: gptimer min_delta_ns corrected Date: Wed, 28 Jan 2009 10:30:52 -0800 Message-ID: <20090128183052.21007.60486.stgit@localhost> References: <20090128181931.21007.73744.stgit@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Return-path: Received: from mho-01-bos.mailhop.org ([63.208.196.178]:61374 "EHLO mho-01-bos.mailhop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751672AbZA1Saz (ORCPT ); Wed, 28 Jan 2009 13:30:55 -0500 In-Reply-To: <20090128181931.21007.73744.stgit@localhost> Sender: linux-omap-owner@vger.kernel.org List-Id: linux-omap@vger.kernel.org To: linux-arm-kernel@lists.arm.linux.org.uk Cc: linux-omap@vger.kernel.org, Aaro Koskinen From: Aaro Koskinen When 32 kHz timer is used the min_delta_ns should be initialized so that it reflects the timer programming cost. A write to the timer device will be usually posted, but it takes roughly 3 cycles before it is effective. If the timer is reprogrammed before that, the CPU will stall until the previous write completes. This was pointed out by Richard Woodruff. Since the lower bound for min_delta_ns is 1000, the change is visible only with tick rates less than 3 MHz. Also note that the old value is incorrect for 32 kHz also due to a rounding error, and it can cause the timer queue to hang (due to clockevent code trying to program the timer with zero ticks). Signed-off-by: Aaro Koskinen Reviewed-by: Richard Woodruff Signed-off-by: Tony Lindgren --- arch/arm/mach-omap2/timer-gp.c | 3 ++- 1 files changed, 2 insertions(+), 1 deletions(-) diff --git a/arch/arm/mach-omap2/timer-gp.c b/arch/arm/mach-omap2/timer-gp.c index ae60363..9fc13a2 100644 --- a/arch/arm/mach-omap2/timer-gp.c +++ b/arch/arm/mach-omap2/timer-gp.c @@ -118,7 +118,8 @@ static void __init omap2_gp_clockevent_init(void) clockevent_gpt.max_delta_ns = clockevent_delta2ns(0xffffffff, &clockevent_gpt); clockevent_gpt.min_delta_ns = - clockevent_delta2ns(1, &clockevent_gpt); + clockevent_delta2ns(3, &clockevent_gpt); + /* Timer internal resynch latency. */ clockevent_gpt.cpumask = cpumask_of(0); clockevents_register_device(&clockevent_gpt);