comedi: comedi_8255: Rework subdevice initialization functions

Comedi drivers can initialize an 8255 subdevice in I/O space by calling
`subdev_8255_init()`, or in memory-mapped I/O space by calling
`subdev_8255_mm_init()`, or by supplying a call-back function pointer
and context to either of those functions. Change it so that a new
function `subdev_8255_cb_init()` shall be called instead when supplying
a callback function and context, and remove the call-back function
parameter from `subdev_8255_init()` and `subdev_8255_mm_init()`.

Also rename `subdev_8255_init()` to `subdev_8255_io_init()`. The
parameters are changing, so might as well rename it at the same time.

Also rename the `regbase` member of `struct subdev_8255_private` to
`context` since this holds the context for the call-back function call.

Cc: Arnd Bergmann <arnd@kernel.org>
Cc: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20230913170712.111719-7-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

comedi: comedi_8254: Replace comedi_8254_init() and comedi_8254_mm_init()

`comedi_8254_init()` and `comedi_8254_mm_init()` return `NULL` on
failure, but the failure is not necessarily due to lack of memory.
Change them to return an `ERR_PTR` value on failure and rename the
functions to make it obvious the API has changed. `comedi_8254_init()`
has been replaced with `comedi_8254_io_alloc()`, and
`comedi_8254_mm_init()` has been replaced with `comedi_8254_mm_alloc()`.

Cc: Arnd Bergmann <arnd@kernel.org>
Cc: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20230913170712.111719-4-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

comedi: Move "comedi_8254.h" to <linux/comedi/comedi_8254.h>

Some of the header files in "drivers/comedi/drivers/" are common enough
to be useful to out-of-tree comedi driver modules. Using them for
out-of-tree module builds is hampered by the headers being outside the
"include/" directory so it is desirable to move them.

There are about a couple of dozen or so Comedi device drivers that use
the "comedi_8254" module to add timers based on the venerable 8254
Programmable Interval Timer chip. The macros and declarations to use
that module are in the "comedi_8254.h" header file in the comedi
"drivers" directory. Move it into "include/linux/comedi/".

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20211117120604.117740-5-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

comedi: Move and rename "8255.h" to <linux/comedi/comedi_8255.h>

Some of the header files in "drivers/comedi/drivers/" are common enough
to be useful to out-of-tree comedi driver modules. Using them for
out-of-tree module builds is hampered by the headers being outside the
"include/" directory so it is desirable to move them.

There are about a couple of dozen Comedi device drivers that use the
"comedi_8255" module to add digital I/O subdevices based on the
venerable 8255 Programmable Peripheral Interface chip. The macros and
declarations to use that module are in the "8255.h" header file in the
comedi "drivers" directory. Move it into "include/linux/comedi/" and
rename it to "comedi_8255.h" for naming consistency reasons.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20211117120604.117740-4-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

comedi: Move the main COMEDI headers

Move the main COMEDI driver headers out of "drivers/comedi/" into new
directory "include/linux/comedi/". These are "comedidev.h",
"comedilib.h", "comedi_pci.h", "comedi_pcmcia.h", and "comedi_usb.h".
Additionally, move the user-space API header "comedi.h" into
"include/uapi/linux/" and add "WITH Linux-syscall-note" to its
SPDX-License-Identifier.

Update the "COMEDI DRIVERS" section of the MAINTAINERS file to account
for these changes.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20211117120604.117740-2-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

staging: comedi: move out of staging directory

The comedi code came into the kernel back in 2008, but traces its
lifetime to much much earlier. It's been polished and buffed and
there's really nothing preventing it from being part of the "real"
portion of the kernel.

So move it to drivers/comedi/ as it belongs there.

Many thanks to the hundreds of developers who did the work to make this
happen.

Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: H Hartley Sweeten <hsweeten@visionengravers.com>
Link: https://lore.kernel.org/r/YHauop4u3sP6lz8j@kroah.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>