linux-kernel - [PATCH v2] Staging: comedi: clean up conditional statement in addi_apci

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Date:	Thu, 13 Feb 2014 19:02:26 -0600
From:	Chase Southwood <chase.southwood@...oo.com>
To:	gregkh@...uxfoundation.org
Cc:	abbotti@....co.uk, hsweeten@...ionengravers.com,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
	Chase Southwood <chase.southwood@...oo.com>
Subject: [PATCH v2] Staging: comedi: clean up conditional statement in addi_apci_3xxx.c

In this conditional statement, if (chan < 16), but the instruction passed
in data[0] is INSN_CONFIG_DIO_QUERY, the function does not return early,
but the else-branch does not get executed either.  As a result, mask
would be used uninitialized in the next line.  We want
comedi_dio_insn_config() to use a chan_mask based on the chanspec for the
INSN_CONFIG_DIO_QUERY instruction, so mask should be initialized to 0.
Then, if instead the instruction is INSN_CONFIG_DIO_{INPUT,OUTPUT}, we
return an error if (chan < 16) as these are invalid instructions for
ports 0 and 1, or update the mask otherwise, so all the io_bits are
modified for port 2.  This ensures that mask is always initialized by the
time it is used.

Signed-off-by: Chase Southwood <chase.southwood@...oo.com>
---

2: Addressed all of the comments provided by Hartley regarding correct
structure of this patch.

Hopefully everything looks better!

 drivers/staging/comedi/drivers/addi_apci_3xxx.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/staging/comedi/drivers/addi_apci_3xxx.c b/drivers/staging/comedi/drivers/addi_apci_3xxx.c
index ceadf8e..1f3b668 100644
--- a/drivers/staging/comedi/drivers/addi_apci_3xxx.c
+++ b/drivers/staging/comedi/drivers/addi_apci_3xxx.c
@@ -680,7 +680,7 @@ static int apci3xxx_dio_insn_config(struct comedi_device *dev,
 				    unsigned int *data)
 {
 	unsigned int chan = CR_CHAN(insn->chanspec);
-	unsigned int mask;
+	unsigned int mask = 0;
 	int ret;

 	/*
@@ -688,12 +688,13 @@ static int apci3xxx_dio_insn_config(struct comedi_device *dev,
 	 * Port 1 (channels 8-15) are always outputs
 	 * Port 2 (channels 16-23) are programmable i/o
 	 */
-	if (chan < 16) {
-		if (data[0] != INSN_CONFIG_DIO_QUERY)
+	if (data[0] != INSN_CONFIG_DIO_QUERY) {
+		/* ignore all other instructions for ports 0 and 1 */
+		if (chan < 16)
 			return -EINVAL;
-	} else {
-		/* changing any channel in port 2 changes the entire port */
-		mask = 0xff0000;
+		else
+			/* changing any channel in port 2 changes the entire port */
+			mask = 0xff0000;
 	}

 	ret = comedi_dio_insn_config(dev, s, insn, data, mask);
-- 
1.8.5.3

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