[U-Boot] [PATCH 1/3] i2c: add i2c_core and prepare for new multibus support

[Simon Glass]

Hi Heiko,

On Wed, Jan 18, 2012 at 10:35 PM, Heiko Schocher <hs at denx.de> wrote:
> Hello Wolfgang, Timur, Simon,
>
> Wolfgang Denk wrote:
>> Dear Simon Glass,
>>
>> In message <CAPnjgZ2kLPfMzzwgHkDJ4eL+wixqLv89+CvdVP7PCcy+XFaqNQ at mail.gmail.com> you wrote:
>>>> I was really hoping we could get rid of the concept of a "current" i2c
>>>> adapter, and just force all drivers to specify the I2C adapter they
>>>> want to use for a given I2C operation. =A0That's how Linux operates, and
>>>> it will prevent stuff like this:
>>> I agree completely, it was one of the things I was going to ask for.
>>> We should add a new parameter to calls instead IMO.
>>
>> Let's do one step at a time.  Now we go for multi-bus support.
>
> Ok.
>
>> Implementing a new, better device interface is one of the next steps,
>> then.
>
> Some thoughts to the subject "get rid of concept of a current i2c"
>
> - First, it would be great to get rid of that ;-)
>
> - 2 reasons why we currently need the info, what is the current
>  i2c adapter/i2c bus:
>
> - U-Boot principle says, don't init a device, if you don't use it.
>  So, if we switch to another i2c adapter or i2c bus (A i2c bus is a
>  combination if one i2c adpater and n i2c muxes), we must deinit
>  the current adapter/bus. Ok, current code didn't this too, but
>  this should a goal to keep in mind ... or we define, that this
>  is not needed.
>
> - If we have i2c muxes, and you don't know your current i2c bus,
>  you must on every i2c access also setup the i2c muxes on this
>  i2c bus ... would we do this really?

Ignoring muxes, we can have more than one i2c adaptor inited at a time
(i.e. de-initing is optional).

Perhaps reword this slightly. U-Boot can have knowledge of a current
adaptor, mux settings and so on, and use this internally within the
i2c layer to optimise performance and redundant i2c traffic. But the
pain is when the concept of a 'current adaptor' is exposed outside the
i2c layer.

>  if we have the current i2c bus info, we just have to check, if
>  we are on this bus, and do the i2c access ... if we are not on
>  this i2c bus, we can deinit it complete (the new i2c_core disconnects
>  for example all i2c muxes on the i2c bus) and init the new bus.
>  All this work is done in a central function i2c_set_bus_numer()

Yes but this function could become internal perhaps.

>
> - Looking in the new multibus i2c_core.c file, we should get rid of
>
>  static unsigned int i2c_cur_bus __attribute__((section(".data"))) =
>                                CONFIG_SYS_SPD_BUS_NUM;
>
>  and "cur_adap" renamed to "cur_i2c_bus" and should be a
>  "struct i2c_bus_hose" pointer.

Sounds good. Heiko do you have time to take over your two patches I
sent and tidy them up, or should I continue?

Regards,
Simon

>
> bye,
> Heiko
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