Re: [RFC] Device: device_get_binding() returns NULL if device fails initialization


Tomasz Bursztyka
 

Hi Daniel,

And that reminds me, that most of our drivers do not set driver API to
NULL if they fail.
But they do return an explicit code which no one care about:
see _sys_device_do_config_level() in kernel/nanokernel/device.c

I think there you can add also a tiny test:

if (device->init(info) < 0) {
info->driver_api = NULL;
}
Good point Tomasz. Might need to be part of the RFC patch that Daniel posted.
The original discussion was actually started about getting rid of returns of
initialization functions.
Ok I missed that discussion.

The idea was that the kernel could not really do
anything when a driver failed initialization, so why not getting rid of returns
to save a few bytes. The burden of determining whether it is a critical error
during init is up to the driver. If there is a critical error, the driver
should assert (and setting driver_api to NULL).

There are situations where there are non-critical erros during initialization.
For example, the I2C driver, failure to set default configuration is not
critical. As long as the developer sets it later, the driver can still function.
However, with the above code, this non-critical error will cause driver_api
to be NULL, which prevents its usage at all. The driver writer should know
whether an error prevents the device from functioning at all. So it should be
up to driver writer to set driver_api to NULL. One can argue that a non-critical
error should not return anything other than 0. But then it is not passing on
the information that there is a non-critical error (though the kernel does not
really care).
Your RFC patch was not clear about that. It would require to change the
init function signature
and all the existing drivers in one go as well.
I hope we don't consider Kernel device API (init and stuff) as part of
"API 1.0".

Tomasz

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