comedi: pcl818: Add sanity checks for I/O base address

comedi: pcl818: Add sanity checks for I/O base address

The "pcl818" driver uses an admin-supplied configuration option
(`it->options[0]`) to configure the I/O port base address of a board in
the PCL-818 series.  It currently allows any base address to be
configured but the hardware devices only support base addresses
(configured by on-board DIP switches) from 0 to 0x3F0 on 16-byte
boundaries.  If the board has a FIFO and jumper JP6 is in the "Enabled"
(default) position, then the base address needs to be on a 32-byte
boundary and the length of the I/O port region will be 32 (to allow
access to the FIFO registers) instead of 16.  The state of jumper JP6 is
unknown, so if the board has a FIFO device and is being configured on an
odd 16-byte boundary, assume that jumper JP6 is in the "Disabled"
position (to disallow access to the FIFO registers).

Add a sanity check to ensure the device is not configured at an
unsupported base address.

If the board has a FIFO and is configured on an odd 16-byte boundary,
log a reminder that JP6 needs to be in the "Disabled" position for
correct operation.  If the board has a FIFO and is configured on an even
16-byte boundary and the configuration option has been set to use the
FIFO (`it->options[2] == -1`), log a reminder that JP6 needs to be in
the "Enabled" position.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://patch.msgid.link/20260130170416.49994-39-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>