commit e03b29b55f upstream.
Some of the hardware registers of the DMM-32-AT board are multiplexed,
using the least significant two bits of the Miscellaneous Control
register to select the function of registers at offsets 12 to 15:
00 => 8254 timer/counter registers are accessible
01 => 8255 digital I/O registers are accessible
10 => Reserved
11 => Calibration registers are accessible
The interrupt service routine (`dmm32at_isr()`) clobbers the bottom two
bits of the register with value 00, which would interfere with access to
the 8255 registers by the `dm32at_8255_io()` function (used for Comedi
instruction handling on the digital I/O subdevice).
Make use of the generic Comedi device spin-lock `dev->spinlock` (which
is otherwise unused by this driver) to serialize access to the
miscellaneous control register and paged registers.
Fixes: 3c501880ac ("Staging: comedi: add dmm32at driver")
Cc: stable@vger.kernel.org
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://patch.msgid.link/20260112162835.91688-1-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2081f7ba69