patch "staging: comedi: ni_mio_common: fix E series ni_ai_insn_read() data" added to staging-next

This is a note to let you know that I've just added the patch titled

staging: comedi: ni_mio_common: fix E series ni_ai_insn_read() data

to my staging git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git
in the staging-next branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will also be merged in the next major kernel release during the merge window.

If you have any questions about this process, please let me know.

From: Ian Abbott <[email protected]>
Date: Mon, 14 Nov 2016 20:16:22 +0000
Subject: staging: comedi: ni_mio_common: fix E series ni_ai_insn_read() data

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.

----
Needs backporting to stable kernels 3.18 onwards.

---
 drivers/staging/comedi/drivers/ni_mio_common.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

index 95435395c746..a974ab772937 100644
@@ -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;
 			}
 		}
 	}

2.10.2