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Subject[PATCH] Add documentation on meaning of -EPROBE_DEFER
Add a bit of documentation on what it means when a driver .probe() hook
returns the -EPROBE_DEFER error code, including the limitation that
-EPROBE_DEFER should be returned as early as possible, before the driver
starts to register child devices.

Also: minor markup fixes in the same file

Signed-off-by: Grant Likely <>
Cc: Jonathan Corbet <>
Cc: Greg Kroah-Hartman <>
Cc: Saravana Kannan <>
Cc: Andy Shevchenko <>
.../driver-api/driver-model/driver.rst | 32 ++++++++++++++++---
1 file changed, 27 insertions(+), 5 deletions(-)

diff --git a/Documentation/driver-api/driver-model/driver.rst b/Documentation/driver-api/driver-model/driver.rst
index baa6a85c8287..63057d9bc8a6 100644
--- a/Documentation/driver-api/driver-model/driver.rst
+++ b/Documentation/driver-api/driver-model/driver.rst
@@ -4,7 +4,6 @@ Device Drivers

See the kerneldoc for the struct device_driver.


@@ -167,9 +166,26 @@ the driver to that device.

A driver's probe() may return a negative errno value to indicate that
the driver did not bind to this device, in which case it should have
-released all resources it allocated::
+released all resources it allocated.
+Optionally, probe() may return -EPROBE_DEFER if the driver depends on
+resources that are not yet available (e.g., supplied by a driver that
+hasn't initialized yet). The driver core will put the device onto the
+deferred probe list and will try to call it again later. If a driver
+must defer, it should return -EPROBE_DEFER as early as possible to
+reduce the amount of time spent on setup work that will need to be
+unwound and reexecuted at a later time.
+.. warning::
+ -EPROBE_DEFER must not be returned if probe() has already created
+ child devices, even if those child devices are removed again
+ in a cleanup path. If -EPROBE_DEFER is returned after a child
+ device has been registered, it may result in an infinite loop of
+ .probe() calls to the same driver.

- void (*sync_state)(struct device *dev);
+ void (*sync_state) (struct device *dev);

sync_state is called only once for a device. It's called when all the consumer
devices of the device have successfully probed. The list of consumers of the
@@ -212,6 +228,8 @@ over management of devices from the bootloader, the usage of sync_state() is
not restricted to that. Use it whenever it makes sense to take an action after
all the consumers of a device have probed.

int (*remove) (struct device *dev);

remove is called to unbind a driver from a device. This may be
@@ -224,11 +242,15 @@ not. It should free any resources allocated specifically for the
device; i.e. anything in the device's driver_data field.

If the device is still present, it should quiesce the device and place
-it into a supported low-power state::
+it into a supported low-power state.

int (*suspend) (struct device *dev, pm_message_t state);

-suspend is called to put the device in a low power state::
+suspend is called to put the device in a low power state.

int (*resume) (struct device *dev);

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