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

[Wolfgang Denk]

Dear ksi at koi8.net,

In message <Pine.LNX.4.64ksi.0902171233390.30435 at home-gw.koi8.net> you wrote:
>
> What is unreadable in that code?

It gets out of control. You don;t see any more how much code gets
generated from that.

> > This is a boot loader with limited resources, not a general purpose
> > OS.
> 
> It doesn't matter. It is much better to have a uniform API for all the
> future developers to use than to multiply horrible hacks and reinventing the
> wheel again and again.

Well, I tell you again that size does matter, and may even be a
killing point when deciding abouut a patch.

> > 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.

[On the other hand I still wonder why I have never seen any such
board appear to me in real life yet. None of the 500+ boards
supported in U-Boot uses any such configuration.]

> And yes, we DO have some boards with switched I2C busses in U-Boot main tree
> so this is NOT a hypothetical situation.

Yes, it is, because none of them needs any such switching before
relocation. And switching is really simple so far.

> > > And the million dollar question -- what is the potential gain?
> > 
> > Indeed. The  same  question  goes  to  you  -  where  is  this  added
> > complexity  really  needed? So far nowhere. Are we just talking about
> > hypothetical cases, or about a real design? How  many  such  designs?
> > Just a single one?
> 
> Please see above.

You did not answer my question.


Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
I express preference for a chronological  sequence  of  events  which
precludes a violence.   - Terry Pratchett, _The Dark Side of the Sun_