The pins a board publishes are visible in /dev and each can be read
through its own node, but surveying a whole board that way means an open
and two ioctls per pin, and the signal and interrupt counters the upper
half keeps are not reachable through any of them.
Adds a list of registered pins and publishes it as /proc/gpio, behind
GPIO_PROCFS: a quality of life view of the same kind as /proc/pinctrl
and /proc/reset. Every common field comes from state the upper half
already holds: the pin type, the value through go_read(), how many times
the pin has been registered for signals, and how many interrupts it has
taken. Lines carry the same key:value tokens in the same order, so the
file is machine parseable.
Lower halves may supply an optional go_describe() adding what only they
can say, such as which pad carries the line or how its trigger is
configured. It writes text into a caller supplied buffer and the upper
half owns the line, so a lower half needs no procfs knowledge. A lower
half without it is listed with the common tokens alone.
The pin type index is bounded before use: it comes from the lower half
and the name table cannot cover a type the enumeration does not define.
A pin that cannot be read reports val:- rather than a zero that would
read as a real level.
procfs_register() appends without checking for duplicates, so the entry
is claimed once for the lifetime of the system rather than whenever the
list is empty; pins come and go at run time.
The name is held in a buffer as long as the one gpio_pin_register()
accepts, so a listing always names the same string as /dev.
The pin type name table is declared without an explicit size so that the
assertion beside it compares against the enumeration and can fail; sized
as [GPIO_NPINTYPES] it would have been tautological.
Documents the entry, its tokens, and how a lower half describes a pin.
Off by default: with GPIO_PROCFS unset the list, the lock and the procfs
entry are compiled out, and go_describe() is one more member at the end
of a structure existing lower halves do not reach.
Assisted-by: Claude:claude-opus-5
Signed-off-by: Justin Hammond <justin@dynam.ac>
1528b470b9