On Fri, Mar 27, 2020 at 10:01 AM Grant Likely <grant.likely@xxxxxxx> wrote: > > 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 <grant.likely@xxxxxxx> > Cc: Jonathan Corbet <corbet@xxxxxxx> > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > Cc: Saravana Kannan <saravanak@xxxxxxxxxx> > Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> > --- > .../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. > > - > 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. The infinite loop is a current implementation behavior. Not an intentional choice. So, maybe we can say the behavior is undefined instead? -Saravana
