[PATCH v3 4/6] pinctrl: Add pinctrl binding for Broadcom Capri SoCs

[Sherman Yin]

On 13-12-16 05:17 AM, Linus Walleij wrote:
> On Sat, Dec 14, 2013 at 2:16 AM, Sherman Yin <syin at broadcom.com> wrote:
>
>>>> +- bias-pull-up:                        Integer. Pull up strength in Ohm:
>>>> +                                       1: 1.2 kOhm
>>>> +                                       2: 1.8 kOhm
>>>> +                                       3: 720 Ohm
>>>> +                                       4: 2.7 kOhm
>>>> +                                       5: 831 Ohm
>>>> +                                       6: 1.08 kOhm
>>>> +                                       7: 568 Ohm
>>>
>>>
>>> Please do not use these custom enumerators 1 thru 7.
>>> Instead say that the argument is given in ohms, so for
>>> example:
>>>
>>> bias-pull-up = <12000>;
>>>
>>> Then translate this into the proper enumerator in your
>>> driver instead.
>>
>> Ok.  The 3 bits in this enumeration correspond to enabling the 3 pull up Rs
>> (1.2k, 1.8k, 2.7k) in parallel, so the enum kind of make sense. But sure I
>> can change it to actual ohms and will error out in the driver if specified
>> value is not one of the 7.
>
> Aha, that's how they do it :-)
>
> Please write this in a comment in the driver because it makes
> it a lot easier to understand what is going on, and e.g. how to
> fuzz an apropriate resistance.

Yes, I plan to explain where those odd numbers come from in this file.

> Can you tell me something about how such resistors are produced
> in silicon?

Sorry I'm not quite sure.  I only know a little bit of the circuitry 
down to the schematic level...

Regards,
Sherman