Re: [PATCH v3 07/12] reset: Add reset_control_get_from_provider_exclusive()

When stacking two reset controllers, the upper one should go through the
proper channels: request exclusive reset controls and use them via the
reset_control_*() APIs.  However, unlike the clock subsystem, which has
of_clk_get_from_provider(), the reset subsystem does not offer a way to
lookup and obtain a reset from a reset provider.

Hence add a public helper reset_control_get_from_provider_exclusive()
to lookup and obtain an exclusive reference to a reset controller, based
on the recently introduced __reset_control_get_from_provider() helper.
This will be used by the R-Car X5H Module Controller driver.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
v3:
  - Replace reset_controller_get_provider() by
    reset_control_get_from_provider_exclusive(),
  - Add kerneldoc,

v2:
  - No changes.
---
 drivers/reset/core.c  | 37 ++++++++++++++++++++++++++++++++-----
 include/linux/reset.h |  8 ++++++++
 2 files changed, 40 insertions(+), 5 deletions(-)

diff --git a/drivers/reset/core.c b/drivers/reset/core.c
index 8af7cd2e8a5029df..6d4c95b3edb18248 100644
--- a/drivers/reset/core.c
+++ b/drivers/reset/core.c

@@ -1141,6 +1141,7 @@ __reset_control_get_from_provider(const struct fwnode_reference_args *args,
                                  bool gpio_fallback,
                                  enum reset_control_flags flags)
 {
+       struct fwnode_handle *fwnode = consumer ?: args->fwnode;
        struct reset_control *rstc = ERR_PTR(-EINVAL);
        struct reset_controller_dev *rcdev;
        int rstc_id = -EINVAL;

@@ -1154,18 +1155,26 @@ __reset_control_get_from_provider(const struct fwnode_reference_args *args,
        if (WARN_ON(args->nargs != rcdev->fwnode_reset_n_cells))
                return ERR_PTR(-EINVAL);

-       if (rcdev->of_xlate && is_of_node(consumer)) {
-               struct device_node *np = to_of_node(consumer);
+       if (rcdev->of_xlate && is_of_node(fwnode)) {
+               struct device_node *np = to_of_node(fwnode);
                struct of_phandle_args of_args;
                int ret;

-               ret = of_parse_phandle_with_args(np,
+               if (consumer) {
+                       ret = of_parse_phandle_with_args(np,
                                         gpio_fallback ? "reset-gpios" : "resets",
                                         gpio_fallback ? "#gpio-cells" : "#reset-cells",
                                         gpio_fallback ? 0 : index,
                                         &of_args);
-               if (ret)
-                       return ERR_PTR(ret);
+                       if (ret)
+                               return ERR_PTR(ret);
+               } else {
+                       of_args.np = of_node_get(np);
+                       of_args.args_count = args->nargs;
+
+                       for (unsigned int i = 0; i < args->nargs; i++)
+                               of_args.args[i] = args->args[i];
+               }

                rstc_id = rcdev->of_xlate(rcdev, &of_args);
                of_node_put(of_args.np);

@@ -1257,6 +1266,24 @@ struct reset_control *__reset_control_get(struct device *dev, const char *id,
 }
 EXPORT_SYMBOL_GPL(__reset_control_get);

+/**
+ * reset_control_get_from_provider_exclusive - Lookup and obtain an exclusive
+ *                                            reference to a reset controller.
+ * @args: Reference to the reset controller provider with all the args like
+ *       reset number
+ *
+ * Returns a struct reset_control or IS_ERR() condition containing errno.
+ * If this function is called more than once for the same reset control it will
+ * return -EBUSY.
+ */
+struct reset_control *
+reset_control_get_from_provider_exclusive(const struct fwnode_reference_args *args)
+{
+       return __reset_control_get_from_provider(args, NULL, 0, false,
+                                                RESET_CONTROL_EXCLUSIVE);
+}
+EXPORT_SYMBOL_GPL(reset_control_get_from_provider_exclusive);
+
 int __reset_control_bulk_get(struct device *dev, int num_rstcs,
                             struct reset_control_bulk_data *rstcs,
                             enum reset_control_flags flags)

diff --git a/include/linux/reset.h b/include/linux/reset.h
index 9c391cf0c82298a0..09ee47b27f88d3b1 100644
--- a/include/linux/reset.h
+++ b/include/linux/reset.h

@@ -90,6 +90,8 @@ struct reset_control *__fwnode_reset_control_get(struct fwnode_handle *fwnode,
                                     const char *id, int index, enum reset_control_flags flags);
 struct reset_control *__reset_control_get(struct device *dev, const char *id,
                                          int index, enum reset_control_flags flags);
+struct reset_control *reset_control_get_from_provider_exclusive(
+                               const struct fwnode_reference_args *args);
 void reset_control_put(struct reset_control *rstc);
 int __reset_control_bulk_get(struct device *dev, int num_rstcs,
                             struct reset_control_bulk_data *rstcs,

@@ -173,6 +175,12 @@ static inline struct reset_control *__reset_control_get(
        return optional ? NULL : ERR_PTR(-ENOTSUPP);
 }

+static inline struct reset_control *reset_control_get_from_provider_exclusive(
+                               const struct fwnode_reference_args *args)
+{
+       return NULL;