From patchwork Thu May 21 00:53:20 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Serge Semin X-Patchwork-Id: 11561963 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id A34E8739 for ; Thu, 21 May 2020 00:54:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 95C3920758 for ; Thu, 21 May 2020 00:54:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727992AbgEUAyV (ORCPT ); Wed, 20 May 2020 20:54:21 -0400 Received: from mail.baikalelectronics.com ([87.245.175.226]:33612 "EHLO mail.baikalelectronics.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727936AbgEUAyQ (ORCPT ); Wed, 20 May 2020 20:54:16 -0400 Received: from localhost (unknown [127.0.0.1]) by mail.baikalelectronics.ru (Postfix) with ESMTP id 2E08C80005E8; Thu, 21 May 2020 00:54:11 +0000 (UTC) X-Virus-Scanned: amavisd-new at baikalelectronics.ru Received: from mail.baikalelectronics.ru ([127.0.0.1]) by localhost (mail.baikalelectronics.ru [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id B5585joA7vdh; Thu, 21 May 2020 03:54:10 +0300 (MSK) From: Serge Semin To: Thomas Gleixner , Thomas Bogendoerfer , Daniel Lezcano CC: Serge Semin , Serge Semin , Alexey Malahov , Paul Burton , Ralf Baechle , Alessandro Zummo , Alexandre Belloni , Arnd Bergmann , Rob Herring , , , , Paul Cercueil , Krzysztof Kozlowski , Geert Uytterhoeven , Randy Dunlap , Claudiu Beznea , Maarten ter Huurne , Vincenzo Frascino , Subject: [PATCH v4 7/7] clocksource: mips-gic-timer: Mark GIC timer as unstable if ref clock changes Date: Thu, 21 May 2020 03:53:20 +0300 Message-ID: <20200521005321.12129-8-Sergey.Semin@baikalelectronics.ru> In-Reply-To: <20200521005321.12129-1-Sergey.Semin@baikalelectronics.ru> References: <20200521005321.12129-1-Sergey.Semin@baikalelectronics.ru> MIME-Version: 1.0 X-ClientProxiedBy: MAIL.baikal.int (192.168.51.25) To mail (192.168.51.25) Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org Currently clocksource framework doesn't support the clocks with variable frequency. Since MIPS GIC timer ticks rate might be unstable on some platforms, we must make sure that it justifies the clocksource requirements. MIPS GIC timer is incremented with the CPU cluster reference clocks rate. So in case if CPU frequency changes, the MIPS GIC tick rate changes synchronously. Due to this the clocksource subsystem can't rely on the timer to measure system clocks anymore. This commit marks the MIPS GIC based clocksource as unstable if reference clock (normally it's a CPU reference clocks) rate changes. The clocksource will execute a watchdog thread, which lowers the MIPS GIC timer rating to zero and fallbacks to a new stable one. Note we don't need to set the CLOCK_SOURCE_MUST_VERIFY flag to the MIPS GIC clocksource since normally the timer is stable. The only reason why it gets unstable is due to the ref clock rate change, which event we detect here in the driver by means of the clocks event notifier. Signed-off-by: Serge Semin Cc: Alexey Malahov Cc: Thomas Bogendoerfer Cc: Paul Burton Cc: Ralf Baechle Cc: Alessandro Zummo Cc: Alexandre Belloni Cc: Arnd Bergmann Cc: Rob Herring Cc: linux-mips@vger.kernel.org Cc: linux-rtc@vger.kernel.org Cc: devicetree@vger.kernel.org --- Changelog v3: - Mark clocksource as unstable instead of lowering its rating. --- drivers/clocksource/Kconfig | 1 + drivers/clocksource/mips-gic-timer.c | 19 ++++++++++++++++++- 2 files changed, 19 insertions(+), 1 deletion(-) diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig index f2142e6bbea3..37a745f3ca91 100644 --- a/drivers/clocksource/Kconfig +++ b/drivers/clocksource/Kconfig @@ -572,6 +572,7 @@ config CLKSRC_VERSATILE config CLKSRC_MIPS_GIC bool depends on MIPS_GIC + select CLOCKSOURCE_WATCHDOG select TIMER_OF config CLKSRC_TANGO_XTAL diff --git a/drivers/clocksource/mips-gic-timer.c b/drivers/clocksource/mips-gic-timer.c index ef12c12c2432..d78ad7b60cdc 100644 --- a/drivers/clocksource/mips-gic-timer.c +++ b/drivers/clocksource/mips-gic-timer.c @@ -24,6 +24,9 @@ static DEFINE_PER_CPU(struct clock_event_device, gic_clockevent_device); static int gic_timer_irq; static unsigned int gic_frequency; +static bool __read_mostly gic_clock_unstable; + +static void git_clocksource_unstable(char *reason); static u64 notrace gic_read_count_2x32(void) { @@ -125,8 +128,10 @@ static int gic_clk_notifier(struct notifier_block *nb, unsigned long action, { struct clk_notifier_data *cnd = data; - if (action == POST_RATE_CHANGE) + if (action == POST_RATE_CHANGE) { + git_clocksource_unstable("ref clock rate change"); on_each_cpu(gic_update_frequency, (void *)cnd->new_rate, 1); + } return NOTIFY_OK; } @@ -172,6 +177,18 @@ static struct clocksource gic_clocksource = { .vdso_clock_mode = VDSO_CLOCKMODE_GIC, }; +static void git_clocksource_unstable(char *reason) +{ + if (gic_clock_unstable) + return; + + gic_clock_unstable = true; + + pr_info("GIC timer is unstable due to %s\n", reason); + + clocksource_mark_unstable(&gic_clocksource); +} + static int __init __gic_clocksource_init(void) { unsigned int count_width;