reset: Add support for shared reset controls

In some SoCs some hw-blocks share a reset control. Add support for this
setup by adding new:

reset_control_get_shared()
devm_reset_control_get_shared()
devm_reset_control_get_shared_by_index()

methods to get a reset_control. Note that this patch omits adding of_
variants, if these are needed later they can be easily added.

This patch also changes the behavior of the existing exclusive
reset_control_get() variants, if these are now called more then once
for the same reset_control they will return -EBUSY. To catch existing
drivers triggering this error (there should not be any) a WARN_ON(1)
is added in this path.

When a reset_control is shared, the behavior of reset_control_assert /
deassert is changed, for shared reset_controls these will work like the
clock-enable/disable and regulator-on/off functions. They will keep a
deassert_count, and only (re-)assert the reset after reset_control_assert
has been called as many times as reset_control_deassert was called.

Calling reset_control_assert without first calling reset_control_deassert
is not allowed on a shared reset control. Calling reset_control_reset is
also not allowed on a shared reset control.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

1 files changed, 48 insertions, 11 deletions

diff --git a/drivers/reset/core.c b/drivers/reset/core.c
index 957750600ff3..72b32bd15549 100644
--- a/drivers/reset/core.c
+++ b/drivers/reset/core.c
@@ -8,6 +8,7 @@
  * the Free Software Foundation; either version 2 of the License, or
  * (at your option) any later version.
  */
+#include <linux/atomic.h>
 #include <linux/device.h>
 #include <linux/err.h>
 #include <linux/export.h>
@@ -29,12 +30,16 @@ static LIST_HEAD(reset_controller_list);
  * @id: ID of the reset controller in the reset
  *      controller device
  * @refcnt: Number of gets of this reset_control
+ * @shared: Is this a shared (1), or an exclusive (0) reset_control?
+ * @deassert_cnt: Number of times this reset line has been deasserted
  */
 struct reset_control {
         struct reset_controller_dev *rcdev;
         struct list_head list;
         unsigned int id;
         unsigned int refcnt;
+        int shared;
+        atomic_t deassert_count;
 };
 
 /**
@@ -91,9 +96,14 @@ EXPORT_SYMBOL_GPL(reset_controller_unregister);
 /**
  * reset_control_reset - reset the controlled device
  * @rstc: reset controller
+ *
+ * Calling this on a shared reset controller is an error.
  */
 int reset_control_reset(struct reset_control *rstc)
 {
+        if (WARN_ON(rstc->shared))
+                return -EINVAL;
+
         if (rstc->rcdev->ops->reset)
                 return rstc->rcdev->ops->reset(rstc->rcdev, rstc->id);
 
@@ -104,26 +114,48 @@ EXPORT_SYMBOL_GPL(reset_control_reset);
 /**
  * reset_control_assert - asserts the reset line
  * @rstc: reset controller
+ *
+ * Calling this on an exclusive reset controller guarantees that the reset
+ * will be asserted. When called on a shared reset controller the line may
+ * still be deasserted, as long as other users keep it so.
+ *
+ * For shared reset controls a driver cannot expect the hw's registers and
+ * internal state to be reset, but must be prepared for this to happen.
  */
 int reset_control_assert(struct reset_control *rstc)
 {
-        if (rstc->rcdev->ops->assert)
-                return rstc->rcdev->ops->assert(rstc->rcdev, rstc->id);
+        if (!rstc->rcdev->ops->assert)
+                return -ENOTSUPP;
 
-        return -ENOTSUPP;
+        if (rstc->shared) {
+                if (WARN_ON(atomic_read(&rstc->deassert_count) == 0))
+                        return -EINVAL;
+
+                if (atomic_dec_return(&rstc->deassert_count) != 0)
+                        return 0;
+        }
+
+        return rstc->rcdev->ops->assert(rstc->rcdev, rstc->id);
 }
 EXPORT_SYMBOL_GPL(reset_control_assert);
 
 /**
  * reset_control_deassert - deasserts the reset line
  * @rstc: reset controller
+ *
+ * After calling this function, the reset is guaranteed to be deasserted.
  */
 int reset_control_deassert(struct reset_control *rstc)
 {
-        if (rstc->rcdev->ops->deassert)
-                return rstc->rcdev->ops->deassert(rstc->rcdev, rstc->id);
+        if (!rstc->rcdev->ops->deassert)
+                return -ENOTSUPP;
 
-        return -ENOTSUPP;
+        if (rstc->shared) {
+                if (atomic_inc_return(&rstc->deassert_count) != 1)
+                        return 0;
+        }
+
+        return rstc->rcdev->ops->deassert(rstc->rcdev, rstc->id);
 }
 EXPORT_SYMBOL_GPL(reset_control_deassert);
 
@@ -144,7 +176,7 @@ EXPORT_SYMBOL_GPL(reset_control_status);
 
 static struct reset_control *__reset_control_get(
                                 struct reset_controller_dev *rcdev,
-                                unsigned int index)
+                                unsigned int index, int shared)
 {
         struct reset_control *rstc;
 
@@ -152,6 +184,9 @@ static struct reset_control *__reset_control_get(
 
         list_for_each_entry(rstc, &rcdev->reset_control_head, list) {
                 if (rstc->id == index) {
+                        if (WARN_ON(!rstc->shared || !shared))
+                                return ERR_PTR(-EBUSY);
+
                         rstc->refcnt++;
                         return rstc;
                 }
@@ -167,6 +202,7 @@ static struct reset_control *__reset_control_get(
         list_add(&rstc->list, &rcdev->reset_control_head);
         rstc->id = index;
         rstc->refcnt = 1;
+        rstc->shared = shared;
 
         return rstc;
 }
@@ -185,7 +221,7 @@ static void __reset_control_put(struct reset_control *rstc)
 }
 
 struct reset_control *__of_reset_control_get(struct device_node *node,
-                                             const char *id, int index)
+                                     const char *id, int index, int shared)
 {
         struct reset_control *rstc;
         struct reset_controller_dev *r, *rcdev;
@@ -235,7 +271,7 @@ struct reset_control *__of_reset_control_get(struct device_node *node,
         }
 
         /* reset_list_mutex also protects the rcdev's reset_control list */
-        rstc = __reset_control_get(rcdev, rstc_id);
+        rstc = __reset_control_get(rcdev, rstc_id, shared);
 
         mutex_unlock(&reset_list_mutex);
 
@@ -265,7 +301,7 @@ static void devm_reset_control_release(struct device *dev, void *res)
 }
 
 struct reset_control *__devm_reset_control_get(struct device *dev,
-                                               const char *id, int index)
+                                     const char *id, int index, int shared)
 {
         struct reset_control **ptr, *rstc;
 
@@ -274,7 +310,8 @@ struct reset_control *__devm_reset_control_get(struct device *dev,
         if (!ptr)
                 return ERR_PTR(-ENOMEM);
 
-        rstc = __of_reset_control_get(dev ? dev->of_node : NULL, id, index);
+        rstc = __of_reset_control_get(dev ? dev->of_node : NULL,
+                                      id, index, shared);
         if (!IS_ERR(rstc)) {
                 *ptr = rstc;
                 devres_add(dev, ptr);