From fbc35b45f9f6a971341b9462c6e94c257e779fb5 Mon Sep 17 00:00:00 2001 From: Grant Likely Date: Fri, 27 Mar 2020 17:01:32 +0000 Subject: 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 Cc: Greg Kroah-Hartman Cc: Jonathan Corbet Cc: Saravana Kannan Cc: Andy Shevchenko Reviewed-by: Andy Shevchenko Signed-off-by: Grant Likely Link: https://lore.kernel.org/r/20200327170132.17275-1-grant.likely@arm.com Signed-off-by: Greg Kroah-Hartman --- Documentation/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 63887b813005..7d5040f6a3d8 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. - Allocation ~~~~~~~~~~ @@ -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); -- cgit