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

[ksi at koi8.net]

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

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