Messages in this thread | | | From | Andy Shevchenko <> | Date | Thu, 28 Jun 2018 01:23:43 +0300 | Subject | Re: [PATCH v2] driver core: add a debugfs entry to show deferred devices |
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On Thu, Jun 28, 2018 at 1:06 AM, Javier Martinez Canillas <javierm@redhat.com> 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> > > --- > > Andy, I didn't carry your Reviewed-by tag because it wasn't clear to me > if you had agreed with the patch or not from your last email.
I just had agreed on the concerns that Greg pointed out to. If it's resolved (*), I'm fine with the change per se. So, my tag still stays
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
(*) At least I'd got the rationale behind it, though it wasn't clear in the previous commit message.
> > 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. > > > drivers/base/dd.c | 29 +++++++++++++++++++++++++++++ > 1 file changed, 29 insertions(+) > > diff --git a/drivers/base/dd.c b/drivers/base/dd.c > index 1435d7281c6..489c484301b 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 +54,7 @@ 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; > static bool initcalls_done; > > /* > @@ -224,6 +226,24 @@ 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 > * > @@ -233,6 +253,9 @@ 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 */ > @@ -242,6 +265,12 @@ 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 > -- > 2.17.1 >
-- With Best Regards, Andy Shevchenko
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