[PATCH v2] reset: make shared pulsed reset controls re-triggerable

[Amjad Ouled-Ameur <aouledameur@baylibre.com>]

The current reset framework API does not allow to release what is done by
reset_control_reset(), IOW decrement triggered_count. Add the new
reset_control_rearm() call to do so.

When reset_control_reset() has been called once, the counter
triggered_count, in the reset framework, is incremented i.e the resource
under the reset is in-use and the reset should not be done again.
reset_control_rearm() would be the way to state that the resource is
no longer used and, that from the caller's perspective, the reset can be
fired again if necessary.

Signed-off-by: Amjad Ouled-Ameur <aouledameur@baylibre.com>
Reported-by: Jerome Brunet <jbrunet@baylibre.com>
---
Change since v1: [0]
* Renamed the new call from reset_control_(array_)resettable to 
reset_control_(array_)rearm
* Open-coded reset_control_array_rearm to check for errors before
decrementing triggered_count because we cannot roll back in case an
error occurs while decrementing one of the rstc.
* Reworded the new call's description.

[0] https://lore.kernel.org/lkml/20201001132758.12280-1-aouledameur@baylibre.com

 drivers/reset/core.c  | 73 +++++++++++++++++++++++++++++++++++++++++++
 include/linux/reset.h |  1 +
 2 files changed, 74 insertions(+)

diff --git a/drivers/reset/core.c b/drivers/reset/core.c
index a2df88e90011..34e89aa0fb5e 100644
--- a/drivers/reset/core.c
+++ b/drivers/reset/core.c
@@ -208,6 +208,39 @@ static int reset_control_array_reset(struct reset_control_array *resets)
 	return 0;
 }
 
+static int reset_control_array_rearm(struct reset_control_array *resets)
+{
+	struct reset_control *rstc;
+	int i;
+
+	for (i = 0; i < resets->num_rstcs; i++) {
+		rstc = resets->rstc[i];
+
+		if (!rstc)
+			continue;
+
+		if (WARN_ON(IS_ERR(rstc)))
+			return -EINVAL;
+
+		if (rstc->shared) {
+			if (WARN_ON(atomic_read(&rstc->deassert_count) != 0))
+				return -EINVAL;
+		} else {
+			if (!rstc->acquired)
+				return -EPERM;
+		}
+	}
+
+	for (i = 0; i < resets->num_rstcs; i++) {
+		rstc = resets->rstc[i];
+
+		if (rstc && rstc->shared)
+			WARN_ON(atomic_dec_return(&rstc->triggered_count) < 0);
+	}
+
+	return 0;
+}
+
 static int reset_control_array_assert(struct reset_control_array *resets)
 {
 	int ret, i;
@@ -325,6 +358,46 @@ int reset_control_reset(struct reset_control *rstc)
 }
 EXPORT_SYMBOL_GPL(reset_control_reset);
 
+/**
+ * reset_control_rearm - allow shared reset line to be re-triggered"
+ * @rstc: reset controller
+ *
+ * On a shared reset line the actual reset pulse is only triggered once for the
+ * lifetime of the reset_control instance, except if this call is used.
+ *
+ * Calls to this function must be balanced with calls to reset_control_reset,
+ * a warning is thrown in case triggered_count ever dips below 0.
+ *
+ * Consumers must not use reset_control_(de)assert on shared reset lines when
+ * reset_control_reset or reset_control_rearm have been used.
+ *
+ * If rstc is NULL the function will just return 0.
+ */
+int reset_control_rearm(struct reset_control *rstc)
+{
+	if (!rstc)
+		return 0;
+
+	if (WARN_ON(IS_ERR(rstc)))
+		return -EINVAL;
+
+	if (reset_control_is_array(rstc))
+		return reset_control_array_rearm(rstc_to_array(rstc));
+
+	if (rstc->shared) {
+		if (WARN_ON(atomic_read(&rstc->deassert_count) != 0))
+			return -EINVAL;
+
+		WARN_ON(atomic_dec_return(&rstc->triggered_count) < 0);
+	} else {
+		if (!rstc->acquired)
+			return -EPERM;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(reset_control_rearm);
+
 /**
  * reset_control_assert - asserts the reset line
  * @rstc: reset controller
diff --git a/include/linux/reset.h b/include/linux/reset.h
index 05aa9f440f48..439fec7112a9 100644
--- a/include/linux/reset.h
+++ b/include/linux/reset.h
@@ -13,6 +13,7 @@ struct reset_control;
 #ifdef CONFIG_RESET_CONTROLLER
 
 int reset_control_reset(struct reset_control *rstc);
+int reset_control_rearm(struct reset_control *rstc);
 int reset_control_assert(struct reset_control *rstc);
 int reset_control_deassert(struct reset_control *rstc);
 int reset_control_status(struct reset_control *rstc);
-- 
2.17.1