Meson8b is a cost reduced variant of the Meson8 SoC. It's package size
is smaller than Meson8.
Unfortunately there are a few key differences which cannot be seen
without close inspection of the code and the public S805 datasheet:
- the GPIOX bank is missing the GPIOX_12, GPIOX_13, GPIOX_14 and
  GPIOX_15 GPIOs
- the GPIOY bank is missing the GPIOY_2, GPIOY_4, GPIOY_5, GPIOY_15 and
  GPIOY_16 GPIOs
- the GPIODV bank is missing all GPIOs except GPIODV_9, GPIODV_24,
  GPIODV_25, GPIODV_26, GPIODV_27, GPIODV_28 and GPIODV_29
- the GPIOZ bank is missing completely
- there is a new GPIO bank called "DIF"

This means that Meson8b only has 83 actual GPIO lines. Without any holes
there would be 130 GPIO lines in total (120 are inherited from Meson8
plus 10 new from the DIF bank).

GPIOs greater GPIOZ_3 (whose ID is 83 - as a reminder: this is exactly
the number of actual GPIO lines on Meson8b and also the value of
meson8b_cbus_pinctrl_data.num_pins) cannot berequested. Using CARD_6
(which used ID 100 prior to this patch, "base of the GPIO controller was
382) as an example:
$ echo 482 > /sys/class/gpio/export
export_store: invalid GPIO 482

This removes all non-existing pins from to dt-bindings header file
(include/dt-bindings/gpio/meson8b-gpio.h). This allows us to have a
consecutive numbering for the GPIO #defines (GPIOY_2 doesn't exist for
example, so previously the GPIOY_3 ID was "GPIOY_1 + 2", after this
patch it is "GPIOY_1 + 1"). As a nice side-effect this means that we get
compile-time (instead of runtime) errors if Meson8b .dts uses a pin that
only exists on Meson8.

Additionally the pinctrl-meson8b driver has to be updated to handle this
new GPIO numbering. By default a struct meson_bank only handles GPIO
banks where the pins are numbered consecutively because it calculates
the bit offsets based on the GPIO IDs.
This is solved by  taking the original BANK() definition and splitting it
into consecutive subsets (X0..11 and X16..21). The bit offsets for each
new bank includes the skipped GPIOs (the definition of the "X0..11" bank
is identical to the old "X" bank apart from the "last IRQ" field, the
definition of the new, split "X16..21" bank takes the original "X" bank
and adds 16 - the start of the new split bank - to the "first IRQ",
pullen bit, pull bit, dir bit, out bit and in bit).

Commit 984cffde ("pinctrl: Fix gpio/pin mapping for Meson8b")
fixed the same issue by setting "ngpio" (of the gpio_chip) to 130.
Unfortunately this broke in db80f0e1

 ("pinctrl: meson: get rid of
unneeded domain structures").
The solution from this patch was considered to be better than the
previous attempt at fixing this because it provides compile-time error
checking for the GPIOs that exist on Meson8 but don't exist on Meson8b.

The following pins were tested on an Odroid-C1 using the sysfs GPIO
interface checking that their value (high or low) could be read:
- GPIOX_0, GPIOX_1, GPIOX_2, GPIOX_3, GPIOX_4, GPIOX_5, GPIOX_6,
  GPIOX_7, GPIOX_8, GPIOX_9, GPIOX_10, GPIOX_11, GPIOX_18, GPIOX_19,
  GPIOX_20, GPIOX_21
- GPIOY_3, GPIOY_7, GPIOY_8
(some of these had to be pulled up because they were low by default,
others were high by default so these had to be pulled down)

Reported-by: Linus Lüssing <linus.luessing@c0d3.blue>
Suggested-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>