lkml.org 
[lkml]   [2018]   [Jul]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v3] driver core: add a debugfs entry to show deferred devices
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 <javierm@redhat.com>
> > Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
> > Reviewed-by: Mark Brown <broonie@kernel.org>
> >
> > ---
> >
> > 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

\
 
 \ /
  Last update: 2018-07-08 15:22    [W:0.032 / U:7.192 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site