[U-Boot] [PATCH] 7/12 Multiadapter/multibus I2C, drivers part 4

[Heiko Schocher]

Hello ksi,

ksi at koi8.net wrote:
> On Thu, 19 Feb 2009, Heiko Schocher wrote:
> 
>> Hello ksi,
>>
>> ksi at koi8.net wrote:
>>> On Wed, 18 Feb 2009, Heiko Schocher wrote:
>>>
>>>> Hello Wolfgang,
>>>>
>>>> Wolfgang Denk wrote:
>>>>> Dear ksi at koi8.net,
>>>>>
>>>>> In message <Pine.LNX.4.64ksi.0902171233390.30435 at home-gw.koi8.net> you wrote:
>>>> [...]
>>>>>>> What makes you insist that we cannot change a variable if we need to
>>>>>>> be able to change one?
>>>>>> It is NOT just variable. My approach uses i2c _BUS_, not _ADAPTER_. And
>>>>>> number of busses can be bigger than number of adapters (e.g. when some
>>>>>> busses a reached via muxes or switches.) When doing i2c_set_current_bus()
>>>>>> you are switching _NOT_ adapters, but busses. That involves not only
>>>>>> changing that global variable but also reprogramming muxes/switches for
>>>>>> i2c_set_current_bus() to be consistent and hardware independent. Otherwise
>>>>>> your code should know if that particular bus it is switching to is directly
>>>>>> connected or switched and check the bus it is switching from for muxes. If
>>>>>> they are switched, your code should disconnect the current bus switches,
>>>>>> then do that i2c_set_current_bus() and connect the switches to the new bus
>>>>>> after that.
>>>>>>
>>>>>> That means that code MUST somehow know the topology to take appropriate
>>>>>> actions and properly configure those switches. That means you should somehow
>>>>>> describe that topology for each and every board in CONFIG_* terms and make
>>>>>> each and every place at U-Boot that invokes _ANY_ i2c function to take care
>>>>>> of that switching.
>>>>> You convinced me. This code must not be used before relocation to RAM,
>>>>> then.
>>>> But is is possible to use that code when running from flash, if
>>>> this current pointer is writeable ...
>>> It is not the pointer that must be writeable, it's what it is pointing to...
>> But in your approach this is also not writeable! So we lost nothing, when
>> using such a pointer.
> 
> No, we did NOT. I can still cal adap[N]->init() and it will init the proper

For what you will do this, when you can;t use the adapter, when running from
flash? See Later, why you cannot use it.

> adapter. It does NOT require any global variables for it, it is
> self-sufficient.

But you could not switch busses, nor work with it, first because
i2c_set_bus_num() don;t work for you and i2c_cur_bus is not writeable,
so _all_ accesses with the API in i2c-core.c like for example

int i2c_read(u_int8_t chip, unsigned int addr, int alen,
                                u_int8_t *buffer, int len)
{
        return(ADAP(i2c_cur_bus)->read(chip, addr, alen, buffer, len));
}

_will_ fail, when running from flash, because i2c_cur_bus is not
writeable!

So why will you initialize all adapters when running from flash?

But this is no problem, when we make i2c_cur_bus or this pointer
I would like to see, writeable. And think about my proposal for
i2c_set_bus_num() and we have there also no problem with calling
init() for an adapter.

bye
Heiko
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