staging: comedi: ni_mio_common: protect register write overflow

Fixes two problems introduced as early as
commit 03aef4b6  ("Staging: comedi: add ni_mio_common code"):
(1) Ensures that the last four bits of NISTC_RTSI_TRIGB_OUT_REG register is
    not unduly overwritten on e-series devices.  On e-series devices, the
    first three of the last four bits are reserved.  The last bit defines
    the output selection of the RGOUT0 pin, otherwise known as
    RTSI_Sub_Selection.  For m-series devices, these last four bits are
    indeed used as the output selection of the RTSI7 pin (and the
    RTSI_Sub_Selection bit for the RGOUT0 pin is moved to the
    RTSI_Trig_Direction register.
(2) Allows all 4 RTSI_BRD lines to be treated as valid sources for RTSI
    lines.

This patch also cleans up the ni_get_rtsi_routing command for readability.

Fixes: 03aef4b6  ("Staging: comedi: add ni_mio_common code")
Signed-off-by: Spencer E. Olson <olsonse@umich.edu>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/ni_mio_common.c

@@ -4980,7 +4980,10 @@ static int ni_valid_rtsi_output_source(struct comedi_device *dev,
 	case NI_RTSI_OUTPUT_G_SRC0:
 	case NI_RTSI_OUTPUT_G_GATE0:
 	case NI_RTSI_OUTPUT_RGOUT0:
-	case NI_RTSI_OUTPUT_RTSI_BRD_0:
+	case NI_RTSI_OUTPUT_RTSI_BRD(0):
+	case NI_RTSI_OUTPUT_RTSI_BRD(1):
+	case NI_RTSI_OUTPUT_RTSI_BRD(2):
+	case NI_RTSI_OUTPUT_RTSI_BRD(3):
 		return 1;
 	case NI_RTSI_OUTPUT_RTSI_OSC:
 		return (devpriv->is_m_series) ? 1 : 0;
@@ -5001,11 +5004,18 @@ static int ni_set_rtsi_routing(struct comedi_device *dev,
 		devpriv->rtsi_trig_a_output_reg |= NISTC_RTSI_TRIG(chan, src);
 		ni_stc_writew(dev, devpriv->rtsi_trig_a_output_reg,
 			      NISTC_RTSI_TRIGA_OUT_REG);
-	} else if (chan < 8) {
+	} else if (chan < NISTC_RTSI_TRIG_NUM_CHAN(devpriv->is_m_series)) {
 		devpriv->rtsi_trig_b_output_reg &= ~NISTC_RTSI_TRIG_MASK(chan);
 		devpriv->rtsi_trig_b_output_reg |= NISTC_RTSI_TRIG(chan, src);
 		ni_stc_writew(dev, devpriv->rtsi_trig_b_output_reg,
 			      NISTC_RTSI_TRIGB_OUT_REG);
+	} else if (chan != NISTC_RTSI_TRIG_OLD_CLK_CHAN) {
+		/* probably should never reach this, since the
+		 * ni_valid_rtsi_output_source above errors out if chan is too
+		 * high
+		 */
+		dev_err(dev->class_dev, "%s: unknown rtsi channel\n", __func__);
+		return -EINVAL;
 	}
 	return 2;
 }
@@ -5021,12 +5031,12 @@ static unsigned int ni_get_rtsi_routing(struct comedi_device *dev,
 	} else if (chan < NISTC_RTSI_TRIG_NUM_CHAN(devpriv->is_m_series)) {
 		return NISTC_RTSI_TRIG_TO_SRC(chan,
 					      devpriv->rtsi_trig_b_output_reg);
-	} else {
-		if (chan == NISTC_RTSI_TRIG_OLD_CLK_CHAN)
+	} else if (chan == NISTC_RTSI_TRIG_OLD_CLK_CHAN) {
 		return NI_RTSI_OUTPUT_RTSI_OSC;
-		dev_err(dev->class_dev, "bug! should never get here?\n");
-		return 0;
 	}
+
+	dev_err(dev->class_dev, "%s: unknown rtsi channel\n", __func__);
+	return -EINVAL;
 }
 
 static int ni_rtsi_insn_config(struct comedi_device *dev,