Dear ksi@koi8.net,
In message Pine.LNX.4.64ksi.0902181400470.5729@home-gw.koi8.net you wrote:
How would you know what to initialize and what not to? We were initializing
I don't know. You probably need some way to encode some kind of routing information that tells you which adapter(s) need to be initialized to reach some specific device.
_ALL_ I2C adapters up to today with a single i2c_init() function. It just
Yes, that's the status quo. And it is not good as is, and shall be changed.
It is easy to initialize just a selected set of adapters in the new code but how do we decide what to initialize and what not to?
Good question. Probably each I2C device will have some list of bus/adapter ID's that need to be up to access it, and that will get shut down afterwards.
Should we add a config option like CONFIG_I2C_INIT_ADAPTERS {1,3,5,9} ? But
No, because we probably do not need to activate all tehse adapters at the same time.
Or should we remove i2c_init() from _ALL_ common places and let board developers to call i2c_adap[X]->init() as they see fit? But that is a big rewrite... And there is another place, cmd_i2c.c that must be taken care of...
You will always call i2c_init() for a specific I2C device.
The code should automatically know which adapters need to be initia- lized to "talk" to that device. Yes, you must somehow describe the I2C bus topology, but a single one-way description for the path from the specific device to the CPU should be sufficient.
There is also no way of DE-initilizing those interfaces so that init is like a gun trigger -- once it is pulled, there is no way to bring the bullet back.
That needs to be changed, too.
And the final question -- what is wrong with initializing all I2C adapters for a handful of boards that have more than one? What is the problem? I can
Initializing things that are not actually needed is bad for many reasons. It takes time, and boot time is critical on many systems. It increases the power consumption, and we have a growing number of mobile devices where power consumption is critical. It carries big potential for "unexpected" behaviour (read: nasty failure modes), and so on.
There are projets around that paid a bite price for not deinitia- lizing devices after use. I2C may be relatively harmless, but we thought the same about USB until it bit. And it bit hard. That's a lesson learned.
make that init_all function a weak alias so if there's some problem with performing total init it can be replaced with board-specific function. But frankly I can not see any problems with initializing all 2-3 adapters for a few multiadapter boards...
A rule is a rule is a rule.
Best regards,
Wolfgang Denk