3.8-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ian Abbott <abbotti@xxxxxxxxx> commit 4c4bc25d0fa6beaf054c0b4c3b324487f266c820 upstream. Tuomas <tvainikk _at_ gmail _dot_ com> reported problems getting meaningful output from a Lab-PC+ in differential mode for AI cmds, but AI insn reads gave correct readings. He tracked it down to two problems, one of which is addressed by this patch. It seems the setting of the channel bits for particular scanning modes was incorrect for differential mode. (Only half the number of channels are available in differential mode; comedi refers to them as channels 0, 1, 2 and 3, but the hardware documentation refers to them as channels 0, 2, 4 and 6.) In differential mode, the setting of the channel enable bits in the command1 register should depend on whether the scan enable bit is set. Effectively, we need to double the comedi channel number when the scan enable bit is not set in differential mode. The scan enable bit gets set when the AI scan mode is `MODE_MULT_CHAN_UP` or `MODE_MULT_CHAN_DOWN`, and gets cleared when the AI scan mode is `MODE_SINGLE_CHAN` or `MODE_SINGLE_CHAN_INTERVAL`. The existing test for whether the comedi channel number needs to be doubled in differential mode is incorrect in `labpc_ai_cmd()`. This patch corrects the test. Thanks to Tuomas for suggesting the fix. Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/staging/comedi/drivers/ni_labpc.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/drivers/staging/comedi/drivers/ni_labpc.c +++ b/drivers/staging/comedi/drivers/ni_labpc.c @@ -1202,7 +1202,8 @@ static int labpc_ai_cmd(struct comedi_de else channel = CR_CHAN(cmd->chanlist[0]); /* munge channel bits for differential / scan disabled mode */ - if (mode != MODE_SINGLE_CHAN && aref == AREF_DIFF) + if ((mode == MODE_SINGLE_CHAN || mode == MODE_SINGLE_CHAN_INTERVAL) && + aref == AREF_DIFF) channel *= 2; devpriv->command1_bits |= ADC_CHAN_BITS(channel); devpriv->command1_bits |= thisboard->ai_range_code[range]; -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html