linux-kernel - [PATCH] reset: Add reset controller API

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Date:   Thu,  1 Oct 2020 15:27:58 +0200
From:   Amjad Ouled-Ameur <aouledameur@...libre.com>
To:     Philipp Zabel <p.zabel@...gutronix.de>
Cc:     Amjad Ouled-Ameur <aouledameur@...libre.com>,
        linux-kernel@...r.kernel.org, linux-amlogic@...ts.infradead.org,
        linux-usb@...r.kernel.org, Jerome Brunet <jbrunet@...libre.com>
Subject: [PATCH] reset: Add reset controller API

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_resettable() 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_resettable() 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.

This patch will fix a usb suspend warning seen on the libretech-cc
related to the shared reset line. This warning was addressed by the 
previously reverted commit 7a410953d1fb ("usb: dwc3: meson-g12a: fix shared
reset control use")

Signed-off-by: Amjad Ouled-Ameur <aouledameur@...libre.com>
Reported-by: Jerome Brunet <jbrunet@...libre.com>
---
 drivers/reset/core.c  | 57 +++++++++++++++++++++++++++++++++++++++++++
 include/linux/reset.h |  1 +
 2 files changed, 58 insertions(+)

diff --git a/drivers/reset/core.c b/drivers/reset/core.c
index 01c0c7aa835c..53653d4b55c4 100644
--- a/drivers/reset/core.c
+++ b/drivers/reset/core.c
@@ -207,6 +207,19 @@ static int reset_control_array_reset(struct reset_control_array *resets)
 	return 0;
 }
 
+static int reset_control_array_resettable(struct reset_control_array *resets)
+{
+	int ret, i;
+
+	for (i = 0; i < resets->num_rstcs; i++) {
+		ret = reset_control_resettable(resets->rstc[i]);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
 static int reset_control_array_assert(struct reset_control_array *resets)
 {
 	int ret, i;
@@ -324,6 +337,50 @@ int reset_control_reset(struct reset_control *rstc)
 }
 EXPORT_SYMBOL_GPL(reset_control_reset);
 
+/**
+ * reset_control_resettable - decrements triggered_count of the controlled device
+ * @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 function is used.
+ * In fact, It decrements triggered_count that makes sure of not allowing
+ * a reset if triggered_count is not null.
+ *
+ * This is a no-op in case triggered_count is already null i.e shared reset line
+ * is ready to be triggered.
+ *
+ * Consumers must not use reset_control_(de)assert on shared reset lines when
+ * reset_control_reset has been used.
+ *
+ * If rstc is NULL it is an optional clear and the function will just
+ * return 0.
+ */
+int reset_control_resettable(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_resettable(rstc_to_array(rstc));
+
+	if (rstc->shared) {
+		if (WARN_ON(atomic_read(&rstc->deassert_count) != 0))
+			return -EINVAL;
+
+		if (atomic_read(&rstc->triggered_count) > 0)
+			atomic_dec(&rstc->triggered_count);
+	} else {
+		if (!rstc->acquired)
+			return -EPERM;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(reset_control_resettable);
+
 /**
  * reset_control_assert - asserts the reset line
  * @rstc: reset controller
diff --git a/include/linux/reset.h b/include/linux/reset.h
index 05aa9f440f48..ffa447d0d1d6 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_resettable(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