[PATCH v3 1/2] Document: dt: binding: imx: update pinctrl doc for imx6sll

[Jacky Bai]

> On Wed, Feb 7, 2018 at 3:07 AM, Bai Ping <ping.bai at nxp.com> wrote:
> 
> > Add pinctrl binding doc update for imx6sll.
> >
> > Signed-off-by: Bai Ping <ping.bai at nxp.com>
> > ---
> > changes v2-v3:
> >  - add generic config binding
> 
> > +Optional Properties:
> > +- drive-strength               Integer. Controls Drive Strength
> > +                                       0: HI-Z
> > +                                       1: 260 ohm at 3.3v, 150
> ohm at 1.8v
> > +                                       2: 130 ohm at 3.3v, 75
> ohm at 1.8v
> > +                                       3: 86 ohm at 3.3v, 50
> ohm at 1.8v
> > +                                       4: 65 ohm at 3.3v, 37
> ohm at 1.8v
> > +                                       5: 52 ohm at 3.3v, 30
> ohm at 1.8v
> > +                                       6: 43 ohm at 3.3v, 25
> ohm at 1.8v
> > +                                       7: 37 ohm at 3.3v, 21
> ohm at 1.8v
> 
> HOW INTERESTING.
> 
> I am discussing this a lot with Lucas Stach right now, and in his SoC i.MX8MQ
> that first resistance is said to be 255 Ohm etc.
> 
> Plus it seems he's missing the figures for 1.8V.
> 
> We're discussing whether this is used for impedance matching and what not.
> We really need someone inside NXP to show us the way.
> 

From the application user guide of pin setting:

The drive strength enable (DSE) can be explained as series resistance between an ideal driver’s output and
its load. To achieve maximal transferred power, the impedance of the driver has to match the load
impedance.


> Anyways, I really need the two of you to discuss this, and I will forward my
> conversation with Lucas to you.
> 
> If you can fish around a bit and tell us what this is used for and how:
> 
> - Is the intended usage for impedance matching?
> - Does it control how many totem-poles are activated on the
>   output pad?
> 
> would all be very grateful.
> 
> > +- drive-open-drain             Bool. Enable Pin Open-drian
> 
> Open-drain?

Sorry, it is a typo, will fix it.

BR
Jacky Bai

> 
> Yours,
> Linus Walleij