env: Pass additional parameters to the env lookup function

In preparation for the multiple environment support, let's introduce two
new parameters to the environment driver lookup function: the priority and
operation.

The operation parameter is meant to identify, obviously, the operation you
might want to perform on the environment.

The priority is a number passed to identify the environment priority you
want to retrieve. The lowest priority parameter (0) will be the primary
source.

Combining the two parameters allow you to support multiple environments
through different priorities, and to change those priorities between read
and writes operations.

This is especially useful to implement migration mechanisms where you want
to always use the same environment first, be it to read or write, while the
common case is more likely to use the same environment it has read from to
write it to.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>

env/env.c

@@ -26,8 +26,33 @@ static struct env_driver *_env_driver_lookup(enum env_location loc)
 	return NULL;
 }
 
-static enum env_location env_get_location(void)
+/**
+ * env_get_location() - Returns the best env location for a board
+ * @op: operations performed on the environment
+ * @prio: priority between the multiple environments, 0 being the
+ *        highest priority
+ *
+ * This will return the preferred environment for the given priority.
+ *
+ * All implementations are free to use the operation, the priority and
+ * any other data relevant to their choice, but must take into account
+ * the fact that the lowest prority (0) is the most important location
+ * in the system. The following locations should be returned by order
+ * of descending priorities, from the highest to the lowest priority.
+ *
+ * Returns:
+ * an enum env_location value on success, a negative error code otherwise
+ */
+static enum env_location env_get_location(enum env_operation op, int prio)
 {
+	/*
+	 * We support a single environment, so any environment asked
+	 * with a priority that is not zero is out of our supported
+	 * bounds.
+	 */
+	if (prio >= 1)
+		return ENVL_UNKNOWN;
+
 	if IS_ENABLED(CONFIG_ENV_IS_IN_EEPROM)
 		return ENVL_EEPROM;
 	else if IS_ENABLED(CONFIG_ENV_IS_IN_FAT)
@@ -54,11 +79,27 @@ static enum env_location env_get_location(void)
 		return ENVL_UNKNOWN;
 }
 
-static struct env_driver *env_driver_lookup(void)
+
+/**
+ * env_driver_lookup() - Finds the most suited environment location
+ * @op: operations performed on the environment
+ * @prio: priority between the multiple environments, 0 being the
+ *        highest priority
+ *
+ * This will try to find the available environment with the highest
+ * priority in the system.
+ *
+ * Returns:
+ * NULL on error, a pointer to a struct env_driver otherwise
+ */
+static struct env_driver *env_driver_lookup(enum env_operation op, int prio)
 {
-	enum env_location loc = env_get_location();
+	enum env_location loc = env_get_location(op, prio);
 	struct env_driver *drv;
 
+	if (loc == ENVL_UNKNOWN)
+		return NULL;
+
 	drv = _env_driver_lookup(loc);
 	if (!drv) {
 		debug("%s: No environment driver for location %d\n", __func__,
@@ -71,83 +112,101 @@ static struct env_driver *env_driver_lookup(void)
 
 int env_get_char(int index)
 {
-	struct env_driver *drv = env_driver_lookup();
-	int ret;
+	struct env_driver *drv;
+	int prio;
 
 	if (gd->env_valid == ENV_INVALID)
 		return default_environment[index];
-	if (!drv)
-		return -ENODEV;
-	if (!drv->get_char)
-		return *(uchar *)(gd->env_addr + index);
-	ret = drv->get_char(index);
-	if (ret < 0) {
-		debug("%s: Environment failed to load (err=%d)\n",
-		      __func__, ret);
+
+	for (prio = 0; (drv = env_driver_lookup(ENVOP_GET_CHAR, prio)); prio++) {
+		int ret;
+
+		if (!drv->get_char)
+			continue;
+
+		ret = drv->get_char(index);
+		if (!ret)
+			return 0;
+
+		debug("%s: Environment %s failed to load (err=%d)\n", __func__,
+		      drv->name, ret);
 	}
 
-	return ret;
+	return -ENODEV;
 }
 
 int env_load(void)
 {
-	struct env_driver *drv = env_driver_lookup();
-	int ret = 0;
+	struct env_driver *drv;
+	int prio;
 
-	if (!drv)
-		return -ENODEV;
-	if (!drv->load)
-		return 0;
-	ret = drv->load();
-	if (ret) {
-		debug("%s: Environment failed to load (err=%d)\n", __func__,
-		      ret);
-		return ret;
+	for (prio = 0; (drv = env_driver_lookup(ENVOP_LOAD, prio)); prio++) {
+		int ret;
+
+		if (!drv->load)
+			continue;
+
+		ret = drv->load();
+		if (!ret)
+			return 0;
+
+		debug("%s: Environment %s failed to load (err=%d)\n", __func__,
+		      drv->name, ret);
 	}
 
-	return 0;
+	return -ENODEV;
 }
 
 int env_save(void)
 {
-	struct env_driver *drv = env_driver_lookup();
-	int ret;
+	struct env_driver *drv;
+	int prio;
 
-	if (!drv)
-		return -ENODEV;
-	if (!drv->save)
-		return -ENOSYS;
-
-	printf("Saving Environment to %s...\n", drv->name);
-	ret = drv->save();
-	if (ret) {
-		debug("%s: Environment failed to save (err=%d)\n", __func__,
-		      ret);
-		return ret;
+	for (prio = 0; (drv = env_driver_lookup(ENVOP_SAVE, prio)); prio++) {
+		int ret;
+
+		if (!drv->save)
+			continue;
+
+		printf("Saving Environment to %s...\n", drv->name);
+		ret = drv->save();
+		if (!ret)
+			return 0;
+
+		debug("%s: Environment %s failed to save (err=%d)\n", __func__,
+		      drv->name, ret);
 	}
 
-	return 0;
+	return -ENODEV;
 }
 
 int env_init(void)
 {
-	struct env_driver *drv = env_driver_lookup();
+	struct env_driver *drv;
 	int ret = -ENOENT;
+	int prio;
+
+	for (prio = 0; (drv = env_driver_lookup(ENVOP_INIT, prio)); prio++) {
+		if (!drv->init)
+			continue;
 
-	if (!drv)
-		return -ENODEV;
-	if (drv->init)
 		ret = drv->init();
+		if (!ret)
+			return 0;
+
+		debug("%s: Environment %s failed to init (err=%d)\n", __func__,
+		      drv->name, ret);
+	}
+
+	if (!prio)
+		return -ENODEV;
+
 	if (ret == -ENOENT) {
 		gd->env_addr = (ulong)&default_environment[0];
 		gd->env_valid = ENV_VALID;
 
 		return 0;
-	} else if (ret) {
-		debug("%s: Environment failed to init (err=%d)\n", __func__,
-		      ret);
-		return ret;
 	}
 
-	return 0;
+	return ret;
 }

include/environment.h

@@ -205,6 +205,14 @@ enum env_location {
 	ENVL_UNKNOWN,
 };
 
+/* value for the various operations we want to perform on the env */
+enum env_operation {
+	ENVOP_GET_CHAR,	/* we want to call the get_char function */
+	ENVOP_INIT,	/* we want to call the init function */
+	ENVOP_LOAD,	/* we want to call the load function */
+	ENVOP_SAVE,	/* we want to call the save function */
+};
+
 struct env_driver {
 	const char *name;
 	enum env_location location;