staging: comedi: ni_tio: Allocate shadow regs for each counter chip

The "ni_tio" module contains code to allocate, destroy and operate on a
`struct ni_gpct_device`, which represents a number of counters spread
over one or more blocks (or "chips").  `struct ni_gpct_device` includes
an array member `regs` holding shadow copies of register values.
Unfortunately, this is currently shared by each block of counters so
they interfere with each other.  This is a problem for the "ni_660x"
module, which has 8 counters spread over 2 blocks.  The `regs` storage
needs to be two-dimensional, indexed by block (chip) number and register
number.  (It does not need to be three-dimensional because the registers
for individual counters are intermingled within the block.)

Change the `regs` member to an array pointer that can be indexed like a
two-dimensional array to access the shadow storage for each register in
each block.  Allocate the storage in `ni_gpct_device_construct()` and
free it in `ni_gpct_device_destroy()`.  (`ni_gpct_device_construct()`
can determine the number of blocks from the `num_counters` and
`counters_per_chip` parameters.)

Add new member `num_chips` to hold the number of chips.  Use that to
check that `chip_index` value is in range in the same places that
check the register offset is in range.

Remove the `counters_per_chip` member of `struct ni_gpct_device` as it
is not needed anywhere and could be easily derived from the
`num_counters` and `num_chips` members if required.

Thanks to GitHub user "raabej" (real name unknown) for an initial
implementation of this in the out-of-tree fork of the Comedi drivers.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/staging/comedi/drivers/ni_tio.h b/drivers/staging/comedi/drivers/ni_tio.h
index 1e85d0a53715..e7b05718df9b 100644
--- a/drivers/staging/comedi/drivers/ni_tio.h
+++ b/drivers/staging/comedi/drivers/ni_tio.h
@@ -107,8 +107,8 @@ struct ni_gpct_device {
 	enum ni_gpct_variant variant;
 	struct ni_gpct *counters;
 	unsigned int num_counters;
-	unsigned int counters_per_chip;
-	unsigned int regs[NITIO_NUM_REGS];
+	unsigned int num_chips;
+	unsigned int (*regs)[NITIO_NUM_REGS]; /* [num_chips][NITIO_NUM_REGS] */
 	spinlock_t regs_lock;		/* protects 'regs' */
 	const struct ni_route_tables *routing_tables; /* link to routes */
 };