The regmap API supports IO port accessors so we can take advantage of
regmap abstractions rather than handling access to the device registers
directly in the driver.

For the PCIe-IDIO-24 series of devices, the following BARs are
available:

    BAR[0]: memory mapped PEX8311
    BAR[1]: I/O mapped PEX8311
    BAR[2]: I/O mapped card registers

There are 24 FET Output lines, 24 Isolated Input lines, and 8 TTL/CMOS
lines (which may be configured for either output or input). The GPIO
lines are exposed by the following card registers:

    Base +0x0-0x2 (Read/Write): FET Outputs
    Base +0xB (Read/Write): TTL/CMOS
    Base +0x4-0x6 (Read): Isolated Inputs
    Base +0x7 (Read): TTL/CMOS

In order for the device to support interrupts, the PLX PEX8311 internal
PCI wire interrupt and local interrupt input must first be enabled.

The following card registers for Change-Of-State may be used:

    Base +0x8-0xA (Read): COS Status Inputs
    Base +0x8-0xA (Write): COS Clear Inputs
    Base +0xB (Read): COS Status TTL/CMOS
    Base +0xB (Write): COS Clear TTL/CMOS
    Base +0xE (Read/Write): COS Enable

The COS Enable register is used to enable/disable interrupts and
configure the interrupt levels; each bit maps to a group of eight inputs
as described below:

    Bit 0: IRQ EN Rising Edge IN0-7
    Bit 1: IRQ EN Rising Edge IN8-15
    Bit 2: IRQ EN Rising Edge IN16-23
    Bit 3: IRQ EN Rising Edge TTL0-7
    Bit 4: IRQ EN Falling Edge IN0-7
    Bit 5: IRQ EN Falling Edge IN8-15
    Bit 6: IRQ EN Falling Edge IN16-23
    Bit 7: IRQ EN Falling Edge TTL0-7

An interrupt is asserted when a change-of-state matching the interrupt
level configuration respective for a particular group of eight inputs
with enabled COS is detected.

The COS Status registers may be read to determine which inputs have
changed; if interrupts were enabled, an IRQ will be generated for the
set bits in these registers. Writing the value read from the COS Status
register back to the respective COS Clear register will clear just those
interrupts.
Reviewed-by: Michael Walle <michael@walle.cc>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/3091e387b1d2eac011a1d84e493663aa2acf982e.1680708357.git.william.gray@linaro.org/Signed-off-by: William Breathitt Gray <william.gray@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>