Re: [PATCH 2/2] Make non-linear GPIO ranges accesible from gpiolib

On Fri, Jun 21, 2013 at 11:17 PM, Stephen Warren [off-list ref] wrote:

When I pushed for the concept of groups, I intended it to mean precisely
one single thing. The points below describe this.

1) A pin is a single pin/ball/pad on the package.

2) Some register fields affect just a single pin. For example, there may
be a register field that affects pin A8's mux setting only.

3) Some register fields affect multiple pins at once. For example,
perhaps one register field affects both pin A8's an pin A7's mux setting
at once.

4) Depending on HW design, all register fields might be of type
described at (2) above, or all of the type described at (3) above, or a
mixture of both. Tegra is a mixture.

5) I expect the concept of a pin group to solely represent the various
groups of pins affected by each register field; in (2) above one pin per
group, in (3) above many pins per group.

Thus, to my mind, a pin group is purely a HW concept, and dictated
purely by HW design.

This we can discuss perpetually it seems.

For Nomadik, as I've pointed out in the past it is actually:

(6): it is one register/set if bits per pin, BUT the register settings
 pertain to physical lines having electrical settings which postulate
 that they be handled in batch or wreak havoc.

I.e. it is a HW limitation in the *silicon* of *all* implementations,
but that is *not* expressed in the register map.

For the practical consequences see __nmk_config_pins if (glitch)
runpath. Handling this as a group makes perfect sense from
a hardware point of view.

Yours,
Linus Walleij