[U-Boot] [PATCH] 0/12 Multiadapter/multibus I2C

[Heiko Schocher]

Hello ksi,

ksi at koi8.net wrote:
> On Mon, 16 Feb 2009, Wolfgang Denk wrote:
>
>   
>> Dear ksi at koi8.net,
>>
>> In message <Pine.LNX.4.64ksi.0902142104100.6240 at home-gw.koi8.net> you wrote:
>>     
>>> OK, please explain how that cur_adap_nr->hwadapnr gets assigned. Please also
>>> explain how can one invoke a function on other adapter than "current".
>>> Remember, i2c_init is quite often called BEFORE the code is relocated to RAM
>>> so you can NOT change "current" adapter.
>>>       
>> We could assign an entry in the global data for it.
>>
>> But then - how often will it bbe necessary to switch adapters before
>> relocation? What is I2C being used for? To read the SPD data for the
>> RAM init code. Which other adapter would be needed?
>>     
>
> I can not tell it right away. There might be several RAM DIMMs with their
> own SPD EPROMS sitting on different busses or something else. It is not like
> we absolutely need this feature right now, urgently but it is so easy to
> implement that it would've been a crime to not to... :)
>
> There is another problem with choosing a proper i2c_init() function with
> i2c_set_bus_num() -- the latter also reprograms I2C multiplexers/switches if
> there are any so you essentially need an initialized adapter to switch to it
> to initialize it. Catch 22...
>   

That would not be a problem:

if we are running from flash we could always init in i2c_set_bus_num()
first the new
controllor to which we switch. And if we are running in ram we can always
check in i2c_set_bus_num() if adap->init_done in i2c_adap_t is 1. If
this is not
so, we first init the bus! With this, it should be possible to get rid
of all this i2c_init
calls all over the code ...

One requirement for this:
All "old" code who directly call i2c_read, i2c_write, ... must, if this new
feature is activated, call a i2c_set_bus_num() before accessing the bus. But
this would be only "work" (grep and fix).

bye

Heiko

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