iio: adc: ad7124: Don't create more channels than the driver can handle

The ad7124-4 and ad7124-8 both support 16 channel registers and assigns
each channel defined in dt statically such a register. While the driver
could be a bit more clever about this, it currently isn't and specifying
more than 16 channels yields broken behaviour. So just refuse to bind in
this situation.

Fixes: b3af341 ("iio: adc: Add ad7124 support")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://patch.msgid.link/1b9a5a1d334e5501294f7f9f9d5893f1cdf1b0ec.1733504533.git.u.kleine-koenig@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Origin: next-20241216~37^2~25, commit:cc597af18092d0e84ccb108c8e4aa0beea26634d

Author: ukleinek

drivers/iio/adc/ad7124.c

@@ -831,6 +831,16 @@ static int ad7124_of_parse_channel_config(struct iio_dev *indio_dev,
 		return -ENODEV;
 	}
 
+	/*
+	 * The driver assigns each logical channel defined in the device tree
+	 * statically one channel register. So only accept 16 such logical
+	 * channels to not treat CONFIG_0 (i.e. the register following
+	 * CHANNEL_15) as an additional channel register. The driver could be
+	 * improved to lift this limitation.
+	 */
+	if (st->num_channels > AD7124_MAX_CHANNELS)
+		return dev_err_probe(indio_dev->dev.parent, -EINVAL, "Too many channels defined\n");
+
 	chan = devm_kcalloc(indio_dev->dev.parent, st->num_channels,
 			    sizeof(*chan), GFP_KERNEL);
 	if (!chan)