Re: [PATCH 1/2] radio: Add radio-timb

["Richard Röjfors" <richard.rojfors@pelagicore.com>]

Hans Verkuil wrote:
>> The first time we run we could definitely do a 4l2_i2c_new_subdev*, but what if I rmmod the driver
>> and insmod it again? When we do the do an open, then v4l2_i2c_new_subdev* would fail because the
>> device is only on the bus and probed. So I would have to look for it anyway. Or am I wrong? I found
>> this like the only generic way(?)
> 
> Not sure I understand you. When you call v4l2_device_unregister any registered
> i2c devices will be automatically unloaded from the i2c bus. So when you do a
> new modprobe, then it is as if you did it for the first time.
> 
> This should work. If not, then let me know and we can look at it.

Thanks for the explanation! It should work, I will update accordingly.

> 
>>> Is there a reason why you want to load them only on first use? It is customary
>>> to load them when this driver is loaded. Exceptions to that may be if the i2c
>>> device needs to load a firmware: this can be slow over i2c and so should be
>>> postponed until the i2c driver is needed for the first time.
>> The main reason is actually that this is a platform device which might come available before the I2C
>> bus in the system. So we postpone the use of the bus until needed, because we know for sure it's
>> available at that point.
> 
> The i2c busses are always initialized first. That's a change that went in a few
> kernel releases ago.

Ok, in this case the I2C bus sits on top of a MFD device which might be installed late to reduce
bootup time.

Bootup time is actually also a reason to keep this code in open rather than in probe.


--Richard