[PATCH v6] reset: add support for non-DT systems

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>

The reset framework only supports device-tree. There are some platforms
however, which need to use it even in legacy, board-file based mode.

An example of such architecture is the DaVinci family of SoCs which
supports both device tree and legacy boot modes and we don't want to
introduce any regressions.

We're currently working on converting the platform from its hand-crafted
clock API to using the common clock framework. Part of the overhaul will
be representing the chip's power sleep controller's reset lines using
the reset framework.

This changeset extends the core reset code with a new reset lookup
entry structure. It contains data allowing the reset core to associate
reset lines with devices by comparing the dev_id and con_id strings.

It also provides a function allowing drivers to register lookup entries
with the framework.

The new lookup function is only called as a fallback in case the
of_node field is NULL and doesn't change anything for current users.

Tested with a dummy reset driver with several lookup entries.

An example lookup table registration from a driver can be found below:

static struct reset_control_lookup foobar_reset_lookup[] = {
	RESET_LOOKUP("foo.0", "foo", 15),
	RESET_LOOKUP("bar.0", NULL,   5),
};

foobar_probe()
{
...

        reset_controller_add_lookup(&rcdev, foobar_reset_lookup,
                                    ARRAY_SIZE(foobar_reset_lookup));

...
}

Cc: Sekhar Nori <nsekhar@xxxxxx>
Cc: Kevin Hilman <khilman@xxxxxxxxxxxx>
Cc: David Lechner <david@xxxxxxxxxxxxxx>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
---
v1 -> v2:
- renamed the new function to __reset_control_get_from_lookup()
- added a missing break; when a matching entry is found
- rearranged the code in __reset_control_get() - we can no longer get to the
  return at the bottom, so remove it and return from
  __reset_control_get_from_lookup() if __of_reset_control_get() fails
- return -ENOENT from reset_contol_get() if we can't find a matching entry,
  prevously returned -EINVAL referred to the fact that we passed a device
  without the of_node which is no longer an error condition
- add a comment about needing a sentinel in the lookup table

v2 -> v3:
- added the reset id number field to the lookup struct so that we don't need
  to rely on the array index

v3 -> v4:
- separated the driver and lookup table registration logic by adding a
  function meant to be called by machine-specific code that adds a lookup
  table to the internal list
- the correct reset controller is now found by first finding the lookup
  table associated with it, then finding the actual reset controller by
  the associated device

v4 -> v5:
- since the first user of this will be the davinci clk driver and it
  already registers clock lookup from within the driver code - allow
  drivers to register lookups with the assumption that the code can be
  extended to make it possible to register entries from machine code as
  well
- simplify the code - only expose a single lookup structure and a simply
  registration function
- add the RESET_LOOKUP macro for brevity

v5 -> v6:
- fixed a potential crash if one of the strings passed to strcmp is NULL
- added a check for NULL dev_id when adding the lookup entry

 drivers/reset/core.c             | 72 +++++++++++++++++++++++++++++++++++++++-
 include/linux/reset-controller.h | 28 ++++++++++++++++
 2 files changed, 99 insertions(+), 1 deletion(-)

diff --git a/drivers/reset/core.c b/drivers/reset/core.c
index da4292e9de97..06fa4907afc4 100644
--- a/drivers/reset/core.c
+++ b/drivers/reset/core.c
@@ -23,6 +23,9 @@
 static DEFINE_MUTEX(reset_list_mutex);
 static LIST_HEAD(reset_controller_list);
 
+static DEFINE_MUTEX(reset_lookup_mutex);
+static LIST_HEAD(reset_lookup_list);
+
 /**
  * struct reset_control - a reset control
  * @rcdev: a pointer to the reset controller device
@@ -148,6 +151,36 @@ int devm_reset_controller_register(struct device *dev,
 }
 EXPORT_SYMBOL_GPL(devm_reset_controller_register);
 
+/**
+ * reset_controller_add_lookup - register a set of lookup entries
+ * @rcdev: initialized reset controller device owning the reset line
+ * @lookup: array of reset lookup entries
+ * @num_entries: number of entries in the lookup array
+ */
+void reset_controller_add_lookup(struct reset_controller_dev *rcdev,
+				 struct reset_control_lookup *lookup,
+				 unsigned int num_entries)
+{
+	struct reset_control_lookup *entry;
+	unsigned int i;
+
+	mutex_lock(&reset_lookup_mutex);
+	for (i = 0; i < num_entries; i++) {
+		entry = &lookup[i];
+
+		if (!entry->dev_id) {
+			pr_warn("%s(): reset lookup entry has no dev_id, skipping\n",
+				__func__);
+			continue;
+		}
+
+		entry->rcdev = rcdev;
+		list_add_tail(&entry->list, &reset_lookup_list);
+	}
+	mutex_unlock(&reset_lookup_mutex);
+}
+EXPORT_SYMBOL_GPL(reset_controller_add_lookup);
+
 static inline struct reset_control_array *
 rstc_to_array(struct reset_control *rstc) {
 	return container_of(rstc, struct reset_control_array, base);
@@ -493,6 +526,43 @@ struct reset_control *__of_reset_control_get(struct device_node *node,
 }
 EXPORT_SYMBOL_GPL(__of_reset_control_get);
 
+static struct reset_control *
+__reset_control_get_from_lookup(struct device *dev, const char *con_id,
+				bool shared, bool optional)
+{
+	const struct reset_control_lookup *lookup;
+	const char *dev_id = dev_name(dev);
+	struct reset_control *rstc = NULL;
+
+	if (!dev)
+		return ERR_PTR(-EINVAL);
+
+	mutex_lock(&reset_lookup_mutex);
+
+	list_for_each_entry(lookup, &reset_lookup_list, list) {
+		if (strcmp(lookup->dev_id, dev_id))
+			continue;
+
+		if ((!con_id && !lookup->con_id) ||
+		    ((con_id && lookup->con_id) &&
+		     !strcmp(con_id, lookup->con_id))) {
+			mutex_lock(&reset_list_mutex);
+			rstc = __reset_control_get_internal(lookup->rcdev,
+							    lookup->index,
+							    shared);
+			mutex_unlock(&reset_list_mutex);
+			break;
+		}
+	}
+
+	mutex_unlock(&reset_lookup_mutex);
+
+	if (!rstc)
+		return optional ? NULL : ERR_PTR(-ENOENT);
+
+	return rstc;
+}
+
 struct reset_control *__reset_control_get(struct device *dev, const char *id,
 					  int index, bool shared, bool optional)
 {
@@ -500,7 +570,7 @@ struct reset_control *__reset_control_get(struct device *dev, const char *id,
 		return __of_reset_control_get(dev->of_node, id, index, shared,
 					      optional);
 
-	return optional ? NULL : ERR_PTR(-EINVAL);
+	return __reset_control_get_from_lookup(dev, id, shared, optional);
 }
 EXPORT_SYMBOL_GPL(__reset_control_get);
 
diff --git a/include/linux/reset-controller.h b/include/linux/reset-controller.h
index adb88f8cefbc..25698f6c1fae 100644
--- a/include/linux/reset-controller.h
+++ b/include/linux/reset-controller.h
@@ -26,6 +26,30 @@ struct module;
 struct device_node;
 struct of_phandle_args;
 
+/**
+ * struct reset_control_lookup - represents a single lookup entry
+ *
+ * @list: internal list of all reset lookup entries
+ * @rcdev: reset controller device controlling this reset line
+ * @index: ID of the reset controller in the reset controller device
+ * @dev_id: name of the device associated with this reset line
+ * @con_id name of the reset line (can be NULL)
+ */
+struct reset_control_lookup {
+	struct list_head list;
+	struct reset_controller_dev *rcdev;
+	unsigned int index;
+	const char *dev_id;
+	const char *con_id;
+};
+
+#define RESET_LOOKUP(_dev_id, _con_id, _index)				\
+	{								\
+		.dev_id = _dev_id,					\
+		.con_id = _con_id,					\
+		.index = _index,					\
+	}
+
 /**
  * struct reset_controller_dev - reset controller entity that might
  *                               provide multiple reset controls
@@ -58,4 +82,8 @@ struct device;
 int devm_reset_controller_register(struct device *dev,
 				   struct reset_controller_dev *rcdev);
 
+void reset_controller_add_lookup(struct reset_controller_dev *rcdev,
+				 struct reset_control_lookup *lookup,
+				 unsigned int num_entries);
+
 #endif
-- 
2.16.1