On Sun, Jul 08, 2018 at 03:21:07PM +0200, Greg Kroah-Hartman wrote: > On Sun, Jul 08, 2018 at 02:32:56AM +0200, Javier Martinez Canillas wrote: > > 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 <[email protected]> > > Reviewed-by: Andy Shevchenko <[email protected]> > > Reviewed-by: Mark Brown <[email protected]> > > > > --- > > > > Changes since RFC v1: > > - Remove unneeded ret variable from deferred_devs_show() > > > > Changes since RFC v2: > > - Use DEFINE_SHOW_ATTRIBUTE() macro. > > - Don't propagate debugfs_create_file() error. > > - Remove IS_ENABLED(CONFIG_DEBUG_FS) guards. > > - Drop RFC prefix. > > > > Changes since v1: > > - Better explain in the commit message why this patch is useful. > > - Rename deferred_devices entry to devices_deferred. > > - Add an exit function and remove the debugfs entry. > > > > Changes since v2: > > - Add Andy Shevchenko and Mark Brown Reviewed-by tag. > > - Rebase on top of Greg's driver-core-next branch. > > > > > > drivers/base/dd.c | 30 ++++++++++++++++++++++++++++++ > > 1 file changed, 30 insertions(+) > > > > diff --git a/drivers/base/dd.c b/drivers/base/dd.c > > index 6ea9c5cece7..140f534ee9c 100644 > > --- a/drivers/base/dd.c > > +++ b/drivers/base/dd.c > > @@ -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 +54,8 @@ 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; > > +static bool initcalls_done; > > Wait, why add this variable? No one uses it that I can see in this > patch, doesn't it create a build warning? > > You did test-build this, right?
I just tested it, it causes a build warning, which implies that you did not test this :( greg k-h
