driver core: Extend deferred probe timeout on driver registration

The deferred probe timer that's used for this currently starts at
late_initcall and runs for driver_deferred_probe_timeout seconds. The
assumption being that all available drivers would be loaded and
registered before the timer expires. This means, the
driver_deferred_probe_timeout has to be pretty large for it to cover the
worst case. But if we set the default value for it to cover the worst
case, it would significantly slow down the average case. For this
reason, the default value is set to 0.

Also, with CONFIG_MODULES=y and the current default values of
driver_deferred_probe_timeout=0 and fw_devlink=on, devices with missing
drivers will cause their consumer devices to always defer their probes.
This is because device links created by fw_devlink defer the probe even
before the consumer driver's probe() is called.

Instead of a fixed timeout, if we extend an unexpired deferred probe
timer on every successful driver registration, with the expectation more
modules would be loaded in the near future, then the default value of
driver_deferred_probe_timeout only needs to be as long as the worst case
time difference between two consecutive module loads.

So let's implement that and set the default value to 10 seconds when
CONFIG_MODULES=y.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Rob Herring <robh@kernel.org>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Will Deacon <will@kernel.org>
Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Kevin Hilman <khilman@kernel.org>
Cc: Thierry Reding <treding@nvidia.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Cc: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Cc: linux-gpio@vger.kernel.org
Cc: linux-pm@vger.kernel.org
Cc: iommu@lists.linux-foundation.org
Reviewed-by: Mark Brown <broonie@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20220429220933.1350374-1-saravanak@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/admin-guide/kernel-parameters.txt

@@ -945,8 +945,10 @@
 			[KNL] Debugging option to set a timeout in seconds for
 			deferred probe to give up waiting on dependencies to
 			probe. Only specific dependencies (subsystems or
-			drivers) that have opted in will be ignored. A timeout of 0
+			drivers) that have opted in will be ignored. A timeout
-			will timeout at the end of initcalls. This option will also
+			of 0 will timeout at the end of initcalls. If the time
+			out hasn't expired, it'll be restarted by each
+			successful driver registration. This option will also
 			dump out devices still on the deferred probe list after
 			retrying.
 

drivers/base/base.h

@@ -159,6 +159,7 @@ extern char *make_class_name(const char *name, struct kobject *kobj);
 extern int devres_release_all(struct device *dev);
 extern void device_block_probing(void);
 extern void device_unblock_probing(void);
+extern void deferred_probe_extend_timeout(void);
 
 /* /sys/devices directory */
 extern struct kset *devices_kset;

drivers/base/dd.c

@@ -256,7 +256,12 @@ static int deferred_devs_show(struct seq_file *s, void *data)
 }
 DEFINE_SHOW_ATTRIBUTE(deferred_devs);
 
+#ifdef CONFIG_MODULES
+int driver_deferred_probe_timeout = 10;
+#else
 int driver_deferred_probe_timeout;
+#endif
+
 EXPORT_SYMBOL_GPL(driver_deferred_probe_timeout);
 static DECLARE_WAIT_QUEUE_HEAD(probe_timeout_waitqueue);
 
@@ -317,6 +322,20 @@ static void deferred_probe_timeout_work_func(struct work_struct *work)
 }
 static DECLARE_DELAYED_WORK(deferred_probe_timeout_work, deferred_probe_timeout_work_func);
 
+void deferred_probe_extend_timeout(void)
+{
+	/*
+	 * If the work hasn't been queued yet or if the work expired, don't
+	 * start a new one.
+	 */
+	if (cancel_delayed_work(&deferred_probe_timeout_work)) {
+		schedule_delayed_work(&deferred_probe_timeout_work,
+				driver_deferred_probe_timeout * HZ);
+		pr_debug("Extended deferred probe timeout by %d secs\n",
+					driver_deferred_probe_timeout);
+	}
+}
+
 /**
  * deferred_probe_initcall() - Enable probing of deferred devices
  *

drivers/base/driver.c

@@ -246,6 +246,7 @@ int driver_register(struct device_driver *drv)
 		return ret;
 	}
 	kobject_uevent(&drv->p->kobj, KOBJ_ADD);
+	deferred_probe_extend_timeout();
 
 	return ret;
 }