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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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.