driver core: add a debugfs entry to show deferred devices (28af109a) · Commits · 戴 / test

With Device Trees (DT), the dependencies of the devices are defined in the DT, then the drivers parse that information to lookup the needed resources that have as dependencies. Since drivers and devices are registered in a non-deterministic way, it is possible that a device that is a dependency has not been registered yet by the time that is looked up. In this case the driver that requires this dependency cannot probe and has to defer it. So the driver core adds it to a list of deferred devices that is iterated again every time that a new driver is probed successfully. For debugging purposes it may be useful to know what are the devices whose probe function was deferred. Add a debugfs entry showing that information. $ cat /sys/kernel/debug/devices_deferred 48070000.i2c:twl@48:bci musb-hdrc.0.auto omapdrm.0 This information could be obtained partially by enabling debugging, but it means that the kernel log has to be parsed and the probe deferral balanced with the successes. This can be error probe and has to be done in a ad-hoc manner by everyone who needs to debug these kind of issues. Since the information is already known by the kernel, just show it to make it easier to debug. Signed-off-by:

Javier Martinez Canillas <javierm@redhat.com> Reviewed-by:

Andy Shevchenko <andy.shevchenko@gmail.com> Reviewed-by:

Mark Brown <broonie@kernel.org> Signed-off-by:

Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/dd.c

+29 −0

Original line number	Diff line number	Diff line
		@@ -16,6 +16,7 @@
		* Copyright (c) 2007-2009 Novell Inc.
		*/

		#include <linux/debugfs.h>
		#include <linux/device.h>
		#include <linux/delay.h>
		#include <linux/dma-mapping.h>
		@@ -53,6 +54,7 @@ static DEFINE_MUTEX(deferred_probe_mutex);
		static LIST_HEAD(deferred_probe_pending_list);
		static LIST_HEAD(deferred_probe_active_list);
		static atomic_t deferred_trigger_count = ATOMIC_INIT(0);
		static struct dentry *deferred_devices;

		/*
		* In some cases, like suspend to RAM or hibernation, It might be reasonable
		@@ -199,6 +201,24 @@ void device_unblock_probing(void)
		driver_deferred_probe_trigger();
		}

		/*
		* deferred_devs_show() - Show the devices in the deferred probe pending list.
		*/
		static int deferred_devs_show(struct seq_file s, void data)
		{
		struct device_private *curr;

		mutex_lock(&deferred_probe_mutex);

		list_for_each_entry(curr, &deferred_probe_pending_list, deferred_probe)
		seq_printf(s, "%s\n", dev_name(curr->device));

		mutex_unlock(&deferred_probe_mutex);

		return 0;
		}
		DEFINE_SHOW_ATTRIBUTE(deferred_devs);

		/**
		* deferred_probe_initcall() - Enable probing of deferred devices
		*
		@@ -208,6 +228,9 @@ void device_unblock_probing(void)
		*/
		static int deferred_probe_initcall(void)
		{
		deferred_devices = debugfs_create_file("devices_deferred", 0444, NULL,
		NULL, &deferred_devs_fops);

		driver_deferred_probe_enable = true;
		driver_deferred_probe_trigger();
		/* Sort as many dependencies as possible before exiting initcalls */
		@@ -216,6 +239,12 @@ static int deferred_probe_initcall(void)
		}
		late_initcall(deferred_probe_initcall);

		static void __exit deferred_probe_exit(void)
		{
		debugfs_remove_recursive(deferred_devices);
		}
		__exitcall(deferred_probe_exit);

		/**
		* device_is_bound() - Check if device is bound to a driver
		* @dev: device to check

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