counter: microchip-tcb-capture: Add support for RC Compare

In Capture mode, the RC register serves as a compare register for the
Timer Counter Channel. When a the Counter Value reaches the RC value, a
RC Compare event occurs (COUNTER_EVENT_THRESHOLD). This patch exposes
the RC register to userspace as the 'compare' Count extension, thus
allowing users to configure the threshold condition for these events.

Acked-by: Bence Csókás <csokas.bence@prolan.hu>
Link: https://lore.kernel.org/r/20250306-introduce-compare-component-v1-2-93993b3dca9c@kernel.org
Signed-off-by: William Breathitt Gray <wbg@kernel.org>

Author: William Breathitt Gray

drivers/counter/microchip-tcb-capture.c

@@ -302,11 +302,39 @@ static int mchp_tc_count_cap_write(struct counter_device *counter,
 	return ret;
 }
 
+static int mchp_tc_count_compare_read(struct counter_device *counter, struct counter_count *count,
+				      u64 *val)
+{
+	struct mchp_tc_data *const priv = counter_priv(counter);
+	u32 cnt;
+	int ret;
+
+	ret = regmap_read(priv->regmap, ATMEL_TC_REG(priv->channel[0], RC), &cnt);
+	if (ret < 0)
+		return ret;
+
+	*val = cnt;
+
+	return 0;
+}
+
+static int mchp_tc_count_compare_write(struct counter_device *counter, struct counter_count *count,
+				       u64 val)
+{
+	struct mchp_tc_data *const priv = counter_priv(counter);
+
+	if (val > U32_MAX)
+		return -ERANGE;
+
+	return regmap_write(priv->regmap, ATMEL_TC_REG(priv->channel[0], RC), val);
+}
+
 static DEFINE_COUNTER_ARRAY_CAPTURE(mchp_tc_cnt_cap_array, 2);
 
 static struct counter_comp mchp_tc_count_ext[] = {
 	COUNTER_COMP_ARRAY_CAPTURE(mchp_tc_count_cap_read, mchp_tc_count_cap_write,
 				   mchp_tc_cnt_cap_array),
+	COUNTER_COMP_COMPARE(mchp_tc_count_compare_read, mchp_tc_count_compare_write),
 };
 
 static struct counter_count mchp_tc_counts[] = {