RE: [PATCH v5 01/10] pinctrl: generic: Add bi-directional and output-enable

[Chris Brandt]

On Monday, May 08, 2017, Andy Shevchenko wrote:
> On Mon, May 8, 2017 at 7:01 PM, jmondi <jacopo@xxxxxxxxxx> wrote:
> > On Sun, May 07, 2017 at 09:52:49AM +0200, Linus Walleij wrote:
> >> On Fri, Apr 28, 2017 at 4:53 PM, Andy Shevchenko
> >> <andy.shevchenko@xxxxxxxxx> wrote:
> >>
> >> > Linus, for me it looks like better to revert that change, until we
> >> > will have clear picture why existing configuration parameters can't
> >> > work.
> >>
> >> Yeah I'll revert the binding for fixes.
> 
> > As it seems we won't be able to proceed with the currently proposed
> solution,
> > would that be acceptable now that we use the "pinmux" property to add
> > flags as BIDIR
> 
> Can you explain what does this *electrically* mean?

Bi-Directional:

For any pin that needs to drive (send) or sense (receive) signals, the pin
mux controller can only enable 1 direction of buffers (in this case, it
only the output buffers). Therefore the appropriate bit in the
'bi-directional' register is set in order to enable the signal path in both
directions (ie, enable the input buffers).


> >  and SWIO_[INPUT|OUTPUT] directly there?

In the hardware manual, there is a list of pin functions that if you want
to use, you cannot use the stand pinmux register method that you use for
all the other pins. Instead, you are instructed to do a different
procedure. If course electrically, input/output buffers are still turned
on/off or whatever, but the root reason of why you need to do this
differently for these specific pin/function is not known.

The "SWIO_" portion of the naming comes from the hardware manual which
refers to this as "Software I/O Control Alternative Mode" (which in my
opinion means the HW guys couldn't get the pin directions/buffers to be set
automatically for some reason, so they decided it's the SW guys problem now
for those pins)


> Second question, what makes it differ to what already exists?

We have 3 different flags (properties) that need to be specified for some
pins in some circumstances.
At first, we just tried to pass this additional information in when
defining what function the pin should be just for those pins whose
direction (ie, buffers) would not be set up automatically.
However, this was rejected and we were told to pick from the existing set
generic properties.
But, 3 different generic pinctrl properties that fit what we needed didn't
exist. So, we used the existing "input-enable" and "output-enable", but
then created "bi-directional".


Chris