From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754729AbdCBRzz (ORCPT ); Thu, 2 Mar 2017 12:55:55 -0500 Received: from mail.free-electrons.com ([62.4.15.54]:47681 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752949AbdCBRz2 (ORCPT ); Thu, 2 Mar 2017 12:55:28 -0500 Date: Thu, 2 Mar 2017 18:54:30 +0100 From: Alexandre Belloni To: Guenter Roeck Cc: Wim Van Sebroeck , Nicolas Ferre , Wenyou.Yang@microchip.com, linux-watchdog@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/4] watchdog: sama5d4: fix race condition Message-ID: <20170302175430.4b3j7ptij525vrhm@piout.net> References: <20170302173114.28508-1-alexandre.belloni@free-electrons.com> <20170302173114.28508-3-alexandre.belloni@free-electrons.com> <20170302174224.GC28554@roeck-us.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20170302174224.GC28554@roeck-us.net> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/03/2017 at 09:42:24 -0800, Guenter Roeck wrote: > On Thu, Mar 02, 2017 at 06:31:12PM +0100, Alexandre Belloni wrote: > > WDT_MR and WDT_CR must not updated within three slow clock periods after > > the last ping (write to WDT_CR or WDT_MR). Ensure enough time has elapsed > > before writing those registers. > > wdt_write() waits for 4 periods to ensure at least 3 edges are seen by the > > IP. > > > > Would it be possible to use min_hw_heartbeat_ms for this purpose ? > I don't think so unless you want the core to also use that delay between __watchdog_ping, watchdog_start, watchdog_set_timeout and watchdog_stop. Currently, it is only between two calls of __watchdog_ping, > Thanks, > Guenter > > > Signed-off-by: Alexandre Belloni > > --- > > drivers/watchdog/sama5d4_wdt.c | 33 +++++++++++++++++++++++++++++---- > > 1 file changed, 29 insertions(+), 4 deletions(-) > > > > diff --git a/drivers/watchdog/sama5d4_wdt.c b/drivers/watchdog/sama5d4_wdt.c > > index 5cee20caca78..362fd229786d 100644 > > --- a/drivers/watchdog/sama5d4_wdt.c > > +++ b/drivers/watchdog/sama5d4_wdt.c > > @@ -6,6 +6,7 @@ > > * Licensed under GPLv2. > > */ > > > > +#include > > #include > > #include > > #include > > @@ -29,6 +30,7 @@ struct sama5d4_wdt { > > struct watchdog_device wdd; > > void __iomem *reg_base; > > u32 mr; > > + unsigned long last_ping; > > }; > > > > static int wdt_timeout = WDT_DEFAULT_TIMEOUT; > > @@ -49,8 +51,29 @@ MODULE_PARM_DESC(nowayout, > > #define wdt_read(wdt, field) \ > > readl_relaxed((wdt)->reg_base + (field)) > > > > -#define wdt_write(wtd, field, val) \ > > - writel_relaxed((val), (wdt)->reg_base + (field)) > > +/* 4 slow clock periods is 4/32768 = 122.07µs*/ > > +#define WDT_DELAY usecs_to_jiffies(123) > > + > > +static void wdt_write(struct sama5d4_wdt *wdt, u32 field, u32 val) > > +{ > > + /* > > + * WDT_CR and WDT_MR must not be modified within three slow clock > > + * periods following a restart of the watchdog performed by a write > > + * access in WDT_CR. > > + */ > > + while (time_before(jiffies, wdt->last_ping + WDT_DELAY)) > > + usleep_range(30, 125); > > + writel_relaxed(val, wdt->reg_base + field); > > + wdt->last_ping = jiffies; > > +} > > + > > +static void wdt_write_nosleep(struct sama5d4_wdt *wdt, u32 field, u32 val) > > +{ > > + if (time_before(jiffies, wdt->last_ping + WDT_DELAY)) > > + udelay(123); > > + writel_relaxed(val, wdt->reg_base + field); > > + wdt->last_ping = jiffies; > > +} > > > > static int sama5d4_wdt_start(struct watchdog_device *wdd) > > { > > @@ -164,11 +187,12 @@ static int sama5d4_wdt_init(struct sama5d4_wdt *wdt) > > * Else, we have to disable it properly. > > */ > > if (wdt_enabled) { > > - wdt_write(wdt, AT91_WDT_MR, wdt->mr); > > + wdt_write_nosleep(wdt, AT91_WDT_MR, wdt->mr); > > } else { > > reg = wdt_read(wdt, AT91_WDT_MR); > > if (!(reg & AT91_WDT_WDDIS)) > > - wdt_write(wdt, AT91_WDT_MR, reg | AT91_WDT_WDDIS); > > + wdt_write_nosleep(wdt, AT91_WDT_MR, > > + reg | AT91_WDT_WDDIS); > > } > > return 0; > > } > > @@ -193,6 +217,7 @@ static int sama5d4_wdt_probe(struct platform_device *pdev) > > wdd->ops = &sama5d4_wdt_ops; > > wdd->min_timeout = MIN_WDT_TIMEOUT; > > wdd->max_timeout = MAX_WDT_TIMEOUT; > > + wdt->last_ping = jiffies; > > > > watchdog_set_drvdata(wdd, wdt); > > > > -- > > 2.11.0 > > -- Alexandre Belloni, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com