From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from metis.ext.pengutronix.de ([2001:6f8:1178:4:290:27ff:fe1d:cc33]) by bombadil.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1Z7NmZ-0002Oy-CM for barebox@lists.infradead.org; Tue, 23 Jun 2015 12:58:36 +0000 Received: from dude.hi.pengutronix.de ([2001:67c:670:100:1d::7]) by metis.ext.pengutronix.de with esmtps (TLS1.2:RSA_AES_128_CBC_SHA1:128) (Exim 4.80) (envelope-from ) id 1Z7NmA-0006G4-NH for barebox@lists.infradead.org; Tue, 23 Jun 2015 14:58:06 +0200 Received: from jbe by dude.hi.pengutronix.de with local (Exim 4.85) (envelope-from ) id 1Z7NmA-00039H-G4 for barebox@lists.infradead.org; Tue, 23 Jun 2015 14:58:06 +0200 From: Juergen Borleis Date: Tue, 23 Jun 2015 14:58:02 +0200 Message-Id: <1435064284-8015-4-git-send-email-jbe@pengutronix.de> In-Reply-To: <1435064284-8015-1-git-send-email-jbe@pengutronix.de> References: <1435064284-8015-1-git-send-email-jbe@pengutronix.de> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "barebox" Errors-To: barebox-bounces+u.kleine-koenig=pengutronix.de@lists.infradead.org Subject: [PATCH 3/5] Watchdog: add a scope value to the watchdog feature To: barebox@lists.infradead.org Sometimes the SoC internal watchdogs are inappropriate to restart the machine in a reliable manner. This change should help to handle more than one watchdog unit by adding a scope parameter. The framework always prefers the watchdog with the widest scope. For example a watchdog which is able to restart the whole machine (SoC + external devices) gets precedence over a watchdog which can restart the SoC only. Signed-off-by: Juergen Borleis --- Documentation/user/user-manual.rst | 1 + Documentation/user/watchdog.rst | 74 ++++++++++++++++++++++++++++++++++++++ common/restart.c | 6 ++++ drivers/watchdog/im28wd.c | 1 + drivers/watchdog/imxwd.c | 1 + drivers/watchdog/wd_core.c | 24 +++++++++++-- include/watchdog.h | 3 ++ 7 files changed, 108 insertions(+), 2 deletions(-) create mode 100644 Documentation/user/watchdog.rst diff --git a/Documentation/user/user-manual.rst b/Documentation/user/user-manual.rst index 0d6daee..8a32469 100644 --- a/Documentation/user/user-manual.rst +++ b/Documentation/user/user-manual.rst @@ -30,6 +30,7 @@ Contents: system-setup reset-reason system-reset + watchdog * :ref:`search` * :ref:`genindex` diff --git a/Documentation/user/watchdog.rst b/Documentation/user/watchdog.rst new file mode 100644 index 0000000..d8e6e76 --- /dev/null +++ b/Documentation/user/watchdog.rst @@ -0,0 +1,74 @@ +.. _watchdog_usage: + +Using a watchdog +---------------- + +Watchdogs are commonly used to prevent bad software from hanging the whole +system for ever. Sometimes a simple approach can help to make a system work +if hanging failures are happen very seldom: just restart the system and do +everything again in the same way as it was done when the system starts the +last time. + +But using a watchdog should always be the 'last resort' to keep a machine +working. The focus should still be on finding and fixing the bug ;) + +A more complex way to use a watchdog in a real-word example is when the state +frameworks comes into play. Then the watchdog's task isn't only to keep the +machine working. It also monitors the whole health of the machine including +hardware and software. Especially something like a firmware update can go +wrong: a wrong firmware was programmed (wrong release or for a different machine), +programming was incomplete due to a user intervention or power fail and so on. + +In this case the watchdog does not just restart the system if the software hangs, +it also provides 'additional' information about the firmware by this restart. +The barebox's state framework is now able to run some kind of state machine to handle +firmware updates in a correct manner: trying the new firmware once and if it fails falling +back to the previous firmware (if available) for example. + +Refer the :ref:`reset_reason` how to detect the reason why the bootloader runs. +This information can be used by the barebox's state framework. + +.. _watchdog_restart_pitfalls: + +Watchdog Pitfalls +~~~~~~~~~~~~~~~~~ + +If a watchdog triggers a machine restart it suffers from the same issues like +a regular user triggered system machine restart. Refer :ref:`system_reset_pitfalls` +for further details. +So keep this in mind when you select an available watchdog on your machine for +this task. And if you are a hardware designer keep this in mind even more, and +provide a reliable restart source for the software developers and to keep their +headache low. + +Watchdogs from the developers point of view +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Watchdogs gets registered in barebox with a scope. When you register your own +watchdog driver, check its hardware scope carefully and use one of the +definitions from the file ``include/restart.h``. + +The list of defined scopes (defined in file ``include/restart.h``): + +* ``FEATURE_SCOPE_UNKNOWN``: completely useless watchdog, maybe a last resort.. +* ``FEATURE_SCOPE_CPU``: this watchdog is able to restart the core CPU only. + Regarding to the issues in :ref:`system_reset_pitfalls` this kind of watchdog + seems more or less useless. +* ``FEATURE_SCOPE_SOC``: this watchdog is able to restart the whole SoC. Regarding + to the issues in :ref:`system_reset_pitfalls` this scope is more reliable, but + depends on the machine and its hardware design if is able to bring the machine + back into life under every circumstance. +* ``FEATURE_SCOPE_MACHINE``: it is able to restart the whole machine and does + the same like a real ``POR`` does. Best scope and always reliable. + +The selected scope is very important because barebox will always use +the watchdog with the best available scope. + +But that is true only for watchdogs used in barebox and as long barebox is +running. + +If an operating system runs later on, it is the task of this OS to use a watchdog +with a correct scope. Otherwise it suffers from the :ref:`system_reset_pitfalls` +as well. This is even more important if the state framework is used. That means +barebox and the operating system must use the same watchdog in order to check +and change the states correctly. diff --git a/common/restart.c b/common/restart.c index 67797e4..c0c4861 100644 --- a/common/restart.c +++ b/common/restart.c @@ -119,6 +119,12 @@ int restart_remove_handler(void (*func)(struct device_d*), struct device_d *dev) } EXPORT_SYMBOL(restart_remove_handler); +void watchdog_update_global_info(int *scope) +{ + globalvar_add_simple_enum("system.wd.scope", scope, + scope_names, ARRAY_SIZE(scope_names)); +} + static int reset_feature_init(void) { reset_source_update_global_info(); diff --git a/drivers/watchdog/im28wd.c b/drivers/watchdog/im28wd.c index c824a25..918d37a 100644 --- a/drivers/watchdog/im28wd.c +++ b/drivers/watchdog/im28wd.c @@ -197,6 +197,7 @@ static int imx28_wd_probe(struct device_d *dev) if (IS_ERR(priv->regs)) return PTR_ERR(priv->regs); priv->wd.set_timeout = imx28_watchdog_set_timeout; + priv->wd.scope = FEATURE_SCOPE_SOC; if (!(readl(priv->regs + MXS_RTC_STAT) & MXS_RTC_STAT_WD_PRESENT)) { rc = -ENODEV; diff --git a/drivers/watchdog/imxwd.c b/drivers/watchdog/imxwd.c index 3cbae09..60772b1 100644 --- a/drivers/watchdog/imxwd.c +++ b/drivers/watchdog/imxwd.c @@ -185,6 +185,7 @@ static int imx_wd_probe(struct device_d *dev) } priv->ops = ops; priv->wd.set_timeout = imx_watchdog_set_timeout; + priv->wd.scope = FEATURE_SCOPE_SOC; priv->dev = dev; if (IS_ENABLED(CONFIG_WATCHDOG_IMX)) { diff --git a/drivers/watchdog/wd_core.c b/drivers/watchdog/wd_core.c index 3d0cfc6..6386cf3 100644 --- a/drivers/watchdog/wd_core.c +++ b/drivers/watchdog/wd_core.c @@ -13,22 +13,32 @@ */ #include +#include #include #include #include #include +#include +#include /* * Note: this simple framework supports one watchdog only. */ static struct watchdog *watchdog; +static int watchdog_scope; + +void watchdog_update_global_info(int*); int watchdog_register(struct watchdog *wd) { - if (watchdog != NULL) - return -EBUSY; + /* ignore a lower or same priority, it isn't a failure */ + if (wd->scope <= watchdog_scope) + return 0; watchdog = wd; + watchdog_scope = (int)wd->scope; + watchdog_update_global_info(&watchdog_scope); + return 0; } EXPORT_SYMBOL(watchdog_register); @@ -39,6 +49,9 @@ int watchdog_deregister(struct watchdog *wd) return -ENODEV; watchdog = NULL; + watchdog_scope = (int)FEATURE_SCOPE_UNKNOWN; + watchdog_update_global_info(&watchdog_scope); + return 0; } EXPORT_SYMBOL(watchdog_deregister); @@ -55,3 +68,10 @@ int watchdog_set_timeout(unsigned timeout) return watchdog->set_timeout(watchdog, timeout); } EXPORT_SYMBOL(watchdog_set_timeout); + +static int watchdog_capability_init(void) +{ + watchdog_update_global_info(&watchdog_scope); + return 0; +} +coredevice_initcall(watchdog_capability_init); diff --git a/include/watchdog.h b/include/watchdog.h index 7e37b7c..e7047bb 100644 --- a/include/watchdog.h +++ b/include/watchdog.h @@ -13,8 +13,11 @@ #ifndef INCLUDE_WATCHDOG_H # define INCLUDE_WATCHDOG_H +#include + struct watchdog { int (*set_timeout)(struct watchdog *, unsigned); + enum f_scope scope; }; #ifdef CONFIG_WATCHDOG -- 2.1.4 _______________________________________________ barebox mailing list barebox@lists.infradead.org http://lists.infradead.org/mailman/listinfo/barebox