[U-Boot] [PATCH 2/2] WIP: tegra: i2c: Enable new CONFIG_SYS_I2C framework

[Stephen Warren]

On 11/12/2012 11:24 PM, Heiko Schocher wrote:
> Hello Stephen,
> 
> On 08.11.2012 18:05, Stephen Warren wrote:
>> On 11/07/2012 11:47 PM, Heiko Schocher wrote:
>>> On 01.11.2012 18:03, Stephen Warren wrote:
>> ...
>>>> I'd suggest having a CONFIG_SYS_I2C_DRIVERS variable at most, and each
>>>> driver registers an arbitrary number of adapters and/or buses during
>>>> its
>>>> initialization.
>>>
>>> Why should an i2c driver register buses? That is board specific.
>>
>> I don't entirely agree here. Certainly the information is
>> board-specific, but I don't believe that precludes bus registration
>> occurring from the I2C adapter drivers themselves, based on information
>> passed from a board file or device tree.
>>
>> If a particular adapter is instantiated by the board, then there is
>> clearly an I2C bus attached to that adapter. Hence, it's quite
>> reasonable for the adapter itself to register the bus directly attached
>> to it.
> 
> But some i2c drivers have more than one instance... would you for all
> boards register all possible instances of a driver? ...

Register, but perhaps not initialize, seems fine to me.

After all, what if the user wishes to use the I2C adapters for some
custom command; up-front registration of all valid adapters is required
for that, although actual initialization can always be deferred until
if/when the adapter is actually used.

The other issue is that as I pointed out before, the move to define
which I2C (and all other peripheral) adapters are used via device tree
rather than board/config files on some U-Boot platforms seems completely
at odds with not always registering all I2C adapters, at least on the
platforms that use device tree.

>> Following on from there, if there's an I2C bus mux attached to some I2C
>> bus, then there are clearly I2C buses downstream from the bus mux, and
>> the bus mux driver knows exactly how many there are, and can register
>> those buses.
> 
> Here again, why register all possible buses? We are just a bootloader ...

I don't see how being a bootloader is relevant. After all, people can
use for example U-Boot I2C or GPIO commands for board bringup, to
implement HW initialization via custom boot scripts, etc.