[PATCH] counter: 104-quad-8: Support Differential Encoder Cable Status

[William Breathitt Gray <vilhelm.gray@gmail.com>]

The ACCES 104-QUAD-8 series provides status information about the
connection state of the differential encoder cable inputs. This patch
implements support to expose such information from these devices.

Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
---
 .../ABI/testing/sysfs-bus-counter-104-quad-8  | 12 ++++++
 drivers/counter/104-quad-8.c                  | 38 +++++++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-counter-104-quad-8 b/Documentation/ABI/testing/sysfs-bus-counter-104-quad-8
index 46b1f33b2fce..492b3e98f369 100644
--- a/Documentation/ABI/testing/sysfs-bus-counter-104-quad-8
+++ b/Documentation/ABI/testing/sysfs-bus-counter-104-quad-8
@@ -1,3 +1,15 @@
+What:		/sys/bus/counter/devices/counterX/cable_status
+KernelVersion:	5.7
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Differential encoder cable status; bits 0 through 7
+		correspond to channels 1 through 8. Writing a 0 to the
+		corresponding bit will enable the status of the
+		respective channel.
+
+		Logic 0 = cable fault (not connected or loose wires)
+		Logic 1 = cable connection good or cable fault disabled
+
 What:		/sys/bus/counter/devices/counterX/signalY/index_polarity
 KernelVersion:	5.2
 Contact:	linux-iio@vger.kernel.org
diff --git a/drivers/counter/104-quad-8.c b/drivers/counter/104-quad-8.c
index 17e67a84777d..1cbaf7e100a3 100644
--- a/drivers/counter/104-quad-8.c
+++ b/drivers/counter/104-quad-8.c
@@ -56,6 +56,7 @@ struct quad8_iio {
 
 #define QUAD8_REG_CHAN_OP 0x11
 #define QUAD8_REG_INDEX_INPUT_LEVELS 0x16
+#define QUAD8_DIFF_ENCODER_CABLE_STATUS 0x17
 /* Borrow Toggle flip-flop */
 #define QUAD8_FLAG_BT BIT(0)
 /* Carry Toggle flip-flop */
@@ -1268,6 +1269,42 @@ static struct counter_count quad8_counts[] = {
 	QUAD8_COUNT(7, "Channel 8 Count")
 };
 
+static ssize_t quad8_cable_status_read(struct counter_device *counter,
+				       void *private, char *buf)
+{
+	const struct quad8_iio *const priv = counter->priv;
+	unsigned int status;
+
+	status = inb(priv->base + QUAD8_DIFF_ENCODER_CABLE_STATUS);
+
+	return sprintf(buf, "0x%X\n", status);
+}
+
+static ssize_t quad8_cable_status_write(struct counter_device *counter,
+					void *private, const char *buf,
+					size_t len)
+{
+	struct quad8_iio *const priv = counter->priv;
+	u8 enable;
+	int ret;
+
+	ret = kstrtou8(buf, 0, &enable);
+	if (ret)
+		return ret;
+
+	outb(enable, priv->base + QUAD8_DIFF_ENCODER_CABLE_STATUS);
+
+	return len;
+}
+
+static const struct counter_device_ext quad8_device_ext[] = {
+	{
+		.name = "cable_status",
+		.read = quad8_cable_status_read,
+		.write = quad8_cable_status_write
+	}
+};
+
 static int quad8_probe(struct device *dev, unsigned int id)
 {
 	struct iio_dev *indio_dev;
@@ -1304,6 +1341,7 @@ static int quad8_probe(struct device *dev, unsigned int id)
 	quad8iio->counter.num_counts = ARRAY_SIZE(quad8_counts);
 	quad8iio->counter.signals = quad8_signals;
 	quad8iio->counter.num_signals = ARRAY_SIZE(quad8_signals);
+	quad8iio->counter.ext = quad8_device_ext;
 	quad8iio->counter.priv = quad8iio;
 	quad8iio->base = base[id];
 
-- 
2.24.1