staging: comedi: ni_mio_common: fix E series ni_ai_insn_read() data
authorIan Abbott <abbotti@mev.co.uk>
Mon, 14 Nov 2016 20:16:22 +0000 (20:16 +0000)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Tue, 15 Nov 2016 10:04:21 +0000 (11:04 +0100)
Commit 0557344e2149 ("staging: comedi: ni_mio_common: fix local var for
32-bit read") changed the type of local variable `d` from `unsigned
short` to `unsigned int` to fix a bug introduced in
commit 9c340ac934db ("staging: comedi: ni_stc.h: add read/write
callbacks to struct ni_private") when reading AI data for NI PCI-6110
and PCI-6111 cards.  Unfortunately, other parts of the function rely on
the variable being `unsigned short` when an offset value in local
variable `signbits` is added to `d` before writing the value to the
`data` array:

d += signbits;
   data[n] = d;

The `signbits` variable will be non-zero in bipolar mode, and is used to
convert the hardware's 2's complement, 16-bit numbers to Comedi's
straight binary sample format (with 0 representing the most negative
voltage).  This breaks because `d` is now 32 bits wide instead of 16
bits wide, so after the addition of `signbits`, `data[n]` ends up being
set to values above 65536 for negative voltages.  This affects all
supported "E series" cards except PCI-6143 (and PXI-6143). Fix it by
ANDing the value written to the `data[n]` with the mask 0xffff.

Fixes: 0557344e2149 ("staging: comedi: ni_mio_common: fix local var for 32-bit read")
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Cc: <stable@vger.kernel.org>
----
Needs backporting to stable kernels 3.18 onwards.
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
drivers/staging/comedi/drivers/ni_mio_common.c

index 95435395c746cee9261604ea2fc2a8587d07eb95..a974ab77293772cc5e44f6467829c9f1502fe114 100644 (file)
@@ -1875,7 +1875,7 @@ static int ni_ai_insn_read(struct comedi_device *dev,
                                return -ETIME;
                        }
                        d += signbits;
-                       data[n] = d;
+                       data[n] = d & 0xffff;
                }
        } else if (devpriv->is_6143) {
                for (n = 0; n < insn->n; n++) {
@@ -1924,9 +1924,8 @@ static int ni_ai_insn_read(struct comedi_device *dev,
                                data[n] = dl;
                        } else {
                                d = ni_readw(dev, NI_E_AI_FIFO_DATA_REG);
-                               /* subtle: needs to be short addition */
                                d += signbits;
-                               data[n] = d;
+                               data[n] = d & 0xffff;
                        }
                }
        }