comedi: comedi_8254: Use a call-back function for register access

Rework the comedi_8254 module to use a call-back function for register
access.  This will make it easier to isolate the parts that will depend
on the `CONFIG_HAS_IOPORT` macro being defined and also allows the
possibility of supplying an external callback function during
initialization by a variant of the `comedi_8254_init()` and
`comedi_8254_mm_init()` functions, although that has not been
implemented yet.

The `struct comedi_8254` members have been changed to use a pointer to a
callback function and a context of type `unsigned long`.  The
`comedi_8254_init()` and `comedi_8254_mm_init()` functions use an
internal callback function and set the context to the base address of
the registers (for `comedi_8254_mm_init()` that involves converting a
`void __iomem *` to `unsigned long`).

A minor change to `dio200_subdev_8254_offset()` in the
amplc_dio200_common module has been made due to the changes in `struct
comedi_8254`.

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/20230913170712.111719-3-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 18 insertions, 4 deletions

diff --git a/include/linux/comedi/comedi_8254.h b/include/linux/comedi/comedi_8254.h
index d8264417e53c..18d12321c87d 100644
--- a/include/linux/comedi/comedi_8254.h
+++ b/include/linux/comedi/comedi_8254.h
@@ -57,10 +57,24 @@ struct comedi_subdevice;
 /* counter maps zero to 0x10000 */
 #define I8254_MAX_COUNT			0x10000
 
+struct comedi_8254;
+
+/**
+ * typedef comedi_8254_iocb_fn - call-back function type for 8254 register access
+ * @i8254:		pointer to struct comedi_8254
+ * @dir:		direction (0 = read, 1 = write)
+ * @reg:		register number
+ * @val:		value to write
+ *
+ * Return: Register value when reading, 0 when writing.
+ */
+typedef unsigned int comedi_8254_iocb_fn(struct comedi_8254 *i8254, int dir,
+					 unsigned int reg, unsigned int val);
+
 /**
  * struct comedi_8254 - private data used by this module
- * @iobase:		PIO base address of the registers (in/out)
- * @mmio:		MMIO base address of the registers (read/write)
+ * @iocb:		I/O call-back function for register access
+ * @context:		context for register access (e.g. a base address)
  * @iosize:		I/O size used to access the registers (b/w/l)
  * @regshift:		register gap shift
  * @osc_base:		cascaded oscillator speed in ns
@@ -76,8 +90,8 @@ struct comedi_subdevice;
  * @insn_config:	driver specific (*insn_config) callback
  */
 struct comedi_8254 {
-	unsigned long iobase;
-	void __iomem *mmio;
+	comedi_8254_iocb_fn *iocb;
+	unsigned long context;
 	unsigned int iosize;
 	unsigned int regshift;
 	unsigned int osc_base;