If this call receives an invalid device pointer as argument it
assumes that the `device` is not ready for usage.
This routine is currently called by two device specific APIs:
- device_usable_check(const struct device *dev)
- device_is_ready(const struct device *dev)
The device-specific APIs documentation claims that these two
routines must be called with a device pointer captured from
DEVICE_DT_GET(). So passing NULL is a violation of the rule.
Nevertheless, is quite common in drivers to assign NULL to
a device pointer if the corresponding DT property has not been
found (e.g. a not used gpio interrupt declaration for a given
device instance) and seems legit to interpret this condition
same as the device is not ready for usage.
Signed-off-by: Armando Visconti <armando.visconti@st.com>
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