Messages in this thread | | | Subject | Re: [PATCH v3] driver core: add a debugfs entry to show deferred devices | From | Javier Martinez Canillas <> | Date | Sun, 8 Jul 2018 15:33:55 +0200 |
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On 07/08/2018 03:22 PM, Greg Kroah-Hartman wrote: > 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? >>
Argh, sorry about that. It was my bad when doing the conflict resolution. This variable got removed by commit 0a50f61c4fb ("drivers: base: initcall_debug logs for driver probe times") that made the patch to not apply cleanly anymore.
>> You did test-build this, right? > > I just tested it, it causes a build warning, which implies that you did > not test this :( >
I did but missed the build warning.
> greg k-h >
Best regards, -- Javier Martinez Canillas Software Engineer - Desktop Hardware Enablement Red Hat
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