#include <sys/bus.h> int
DEVICE_PROBE (device_t dev);
method should probe to see if the device is present.
It should return 0 if the device exists,
if it cannot be found.
If some other error happens during the probe (such as a memory
allocation failure), an appropriate error code should be returned.
cases where more than one driver matches a device, a priority value can
In this case, success codes are values less than or equal
to zero with the highest value representing the best match.
codes are represented by positive values and the regular
codes should be used for the purpose.
If a driver returns a success code which is less than zero, it must
not assume that it will be the same driver which is attached to the
In particular, it must not assume that any values stored in
the softc structure will be available for its attach method and any
resources allocated during probe must be released and re-allocated
if the attach method is called.
In addition it is an absolute requirement that the probe routine have
no side effects whatsoever.
The probe routine may be called more than once before the attach
routine is called.
If a success code of zero is
returned, the driver can assume that it will be the one attached, but
must not hold any resources when the probe routine returns.
A driver may assume that the softc is preserved when it returns
a success code of zero.
A value equal to or less than zero indicates success, greater than
zero indicates an error (errno).
For values equal to or less than
zero: zero indicates highest priority, no further probing is done;
for a value less than zero, the lower the value the lower the
priority, e.g. -100 indicates a lower priority than -50.