From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.99]:49274 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728438AbeJSCBf (ORCPT ); Thu, 18 Oct 2018 22:01:35 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Tao Ren , Linus Walleij , Lei YU , Daniel Lezcano , Sasha Levin Subject: [PATCH 4.18 40/53] clocksource/drivers/fttmr010: Fix set_next_event handler Date: Thu, 18 Oct 2018 19:54:33 +0200 Message-Id: <20181018175423.415418195@linuxfoundation.org> In-Reply-To: <20181018175416.561567978@linuxfoundation.org> References: <20181018175416.561567978@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: 4.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tao Ren [ Upstream commit 4451d3f59f2a6f95e5d205c2d04ea072955d080d ] Currently, the aspeed MATCH1 register is updated to in set_next_event handler, with the assumption that COUNT register value is preserved when the timer is disabled and it continues decrementing after the timer is enabled. But the assumption is wrong: RELOAD register is loaded into COUNT register when the aspeed timer is enabled, which means the next event may be delayed because timer interrupt won't be generated until <0xFFFFFFFF - current_count + cycles>. The problem can be fixed by updating RELOAD register to , and COUNT register will be re-loaded when the timer is enabled and interrupt is generated when COUNT register overflows. The test result on Facebook Backpack-CMM BMC hardware (AST2500) shows the issue is fixed: without the patch, usleep(100) suspends the process for several milliseconds (and sometimes even over 40 milliseconds); after applying the fix, usleep(100) takes averagely 240 microseconds to return under the same workload level. Signed-off-by: Tao Ren Reviewed-by: Linus Walleij Tested-by: Lei YU Signed-off-by: Daniel Lezcano Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- drivers/clocksource/timer-fttmr010.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-) --- a/drivers/clocksource/timer-fttmr010.c +++ b/drivers/clocksource/timer-fttmr010.c @@ -130,13 +130,17 @@ static int fttmr010_timer_set_next_event cr &= ~fttmr010->t1_enable_val; writel(cr, fttmr010->base + TIMER_CR); - /* Setup the match register forward/backward in time */ - cr = readl(fttmr010->base + TIMER1_COUNT); - if (fttmr010->count_down) - cr -= cycles; - else - cr += cycles; - writel(cr, fttmr010->base + TIMER1_MATCH1); + if (fttmr010->count_down) { + /* + * ASPEED Timer Controller will load TIMER1_LOAD register + * into TIMER1_COUNT register when the timer is re-enabled. + */ + writel(cycles, fttmr010->base + TIMER1_LOAD); + } else { + /* Setup the match register forward in time */ + cr = readl(fttmr010->base + TIMER1_COUNT); + writel(cr + cycles, fttmr010->base + TIMER1_MATCH1); + } /* Start */ cr = readl(fttmr010->base + TIMER_CR);