Re: [PATCH] pinctrl: samsung: Allow pin value to be initialized using pinfunc.

[Linus Walleij]

On Fri, Dec 6, 2013 at 12:54 AM, Stephen Warren <swarren@xxxxxxxxxxxxx> wrote:
> On 12/03/2013 02:29 AM, Linus Walleij wrote:

(skipped the conversation on weak hogs, we are on the same page
here, just waiting for someone to start working on it ...)

> Related, I prefer to put /all/ static pinctrl configuration into the
> pinctrl device's "default" state (i.e. use a hog) rather than
> configuring the static pinctrl setup per device, for another reason too:
>
> If a particular IO controller's signals can be routed to n different
> (sets of) pins, then we need to do *both* of the following when setting
> up the pinmux:
>
> a) Configure the pins we want to host those signals to route to/from
> that particular IO controller.
>
> b) Configure any other pins that could route to/from that particular IO
> controller as some other function; either disabled, or routed to/from
> some different IO controller.
>
> That is so that the IO controller's RX/input signals are not connected
> from two different sets of pins at once, which would cause two things to
> driver them. Depending on HW, this could cause on of:
>
> 1) Multiple drivers -> high power usage, or even Silicon damage.
>
> 2) Inconsistent configuration, with the "wrong" set of pins driving the
> IO controller's inputs, and hence the signals on the "correct" pins
> being ignored -> hard to find bug.

I'm following, I think what we need here is to think about additional
behaviours and electronic constraints we can encode into the drivers
and/or the pin tables to safeguard pin states from electronically
unsound states.

That is to say, I prefer the subsystem to be conscious about the
electronic constraints and navigate around them or put up a road
block, rather than trying ti avoid driving into the roadblocks by means
of carefully crafted tables if you get the picture ...

Yours,
Linus Walleij
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