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    SubjectRe: [PATCH] Add documentation on meaning of -EPROBE_DEFER
    On Fri, Mar 27, 2020 at 05:01:32PM +0000, Grant Likely 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

    Greg, can we at least for time being have this documented, means applied?

    FWIW,
    Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

    > Signed-off-by: Grant Likely <grant.likely@arm.com>
    > Cc: Jonathan Corbet <corbet@lwn.net>
    > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    > Cc: Saravana Kannan <saravanak@google.com>
    > Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
    > ---
    > .../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.
    > +
    > +::
    >
    > - 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);
    >
    > --
    > 2.20.1
    >

    --
    With Best Regards,
    Andy Shevchenko


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