[PATCH 1/4] reset: instantiate reset GPIO controller for shared reset-gpios

[Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>]

Devices sharing a reset GPIO could use the reset framework for
coordinated handling of that shared GPIO line.  We have several cases of
such needs, at least for Devicetree-based platforms.

If Devicetree-based device requests a reset line which is missing but
there is a reset-gpios property, instantiate a new "reset-gpio" platform
device which will handle such reset line.  This allows seamless handling
of such shared reset-gpios without need of changing Devicetree binding [1].

The "reset-gpio" driver follows shortly.

Link: https://lore.kernel.org/all/YXi5CUCEi7YmNxXM@xxxxxxxxxxxxxxxxxx/
Cc: Bartosz Golaszewski <brgl@xxxxxxxx>
Cc: Sean Anderson <sean.anderson@xxxxxxxx>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
---
 drivers/reset/core.c             | 70 +++++++++++++++++++++++++++-----
 include/linux/reset-controller.h |  2 +
 2 files changed, 61 insertions(+), 11 deletions(-)

diff --git a/drivers/reset/core.c b/drivers/reset/core.c
index 4d5a78d3c085..a1f0f515a7e0 100644
--- a/drivers/reset/core.c
+++ b/drivers/reset/core.c
@@ -10,9 +10,12 @@
 #include <linux/export.h>
 #include <linux/kernel.h>
 #include <linux/kref.h>
+#include <linux/gpio/consumer.h>
 #include <linux/module.h>
 #include <linux/of.h>
+#include <linux/of_gpio.h>
 #include <linux/acpi.h>
+#include <linux/platform_device.h>
 #include <linux/reset.h>
 #include <linux/reset-controller.h>
 #include <linux/slab.h>
@@ -813,13 +816,59 @@ static void __reset_control_put_internal(struct reset_control *rstc)
 	kref_put(&rstc->refcnt, __reset_control_release);
 }
 
+static int __reset_add_reset_gpio_device(struct device_node *node,
+					 const struct gpio_desc **out)
+{
+	struct platform_device *pdev;
+	int gpio;
+
+	/* Don't care about deprecated '-gpio' suffix. */
+	gpio = of_get_named_gpio(node, "reset-gpios", 0);
+	if (!gpio_is_valid(gpio))
+		return gpio;
+
+	pdev = platform_device_register_data(NULL, "reset-gpio",
+					     PLATFORM_DEVID_AUTO, &node,
+					     sizeof(node));
+	if (!IS_ERR(pdev))
+		*out = gpio_to_desc(gpio);
+
+	return PTR_ERR_OR_ZERO(pdev);
+}
+
+static struct reset_controller_dev *__reset_find_rcdev(const struct of_phandle_args *args,
+						       const void *cookie)
+{
+	struct reset_controller_dev *r, *rcdev;
+
+	lockdep_assert_held(&reset_list_mutex);
+
+	rcdev = NULL;
+	list_for_each_entry(r, &reset_controller_list, list) {
+		if (args && args->np) {
+			if (args->np == r->of_node) {
+				rcdev = r;
+				break;
+			}
+		} else if (cookie) {
+			if (cookie == r->cookie) {
+				rcdev = r;
+				break;
+			}
+		}
+	}
+
+	return rcdev;
+}
+
 struct reset_control *
 __of_reset_control_get(struct device_node *node, const char *id, int index,
 		       bool shared, bool optional, bool acquired)
 {
+	const struct gpio_desc *gpio = NULL;
+	struct of_phandle_args args = {0};
 	struct reset_control *rstc;
-	struct reset_controller_dev *r, *rcdev;
-	struct of_phandle_args args;
+	struct reset_controller_dev *rcdev;
 	int rstc_id;
 	int ret;
 
@@ -839,17 +888,16 @@ __of_reset_control_get(struct device_node *node, const char *id, int index,
 					 index, &args);
 	if (ret == -EINVAL)
 		return ERR_PTR(ret);
-	if (ret)
-		return optional ? NULL : ERR_PTR(ret);
+	if (ret) {
+		ret = __reset_add_reset_gpio_device(node, &gpio);
+		if (ret)
+			return optional ? NULL : ERR_PTR(ret);
+
+		args.args_count = 1; /* reset-gpio has only one reset line */
+	}
 
 	mutex_lock(&reset_list_mutex);
-	rcdev = NULL;
-	list_for_each_entry(r, &reset_controller_list, list) {
-		if (args.np == r->of_node) {
-			rcdev = r;
-			break;
-		}
-	}
+	rcdev = __reset_find_rcdev(&args, gpio);
 
 	if (!rcdev) {
 		rstc = ERR_PTR(-EPROBE_DEFER);
diff --git a/include/linux/reset-controller.h b/include/linux/reset-controller.h
index 0fa4f60e1186..c0a99a8ea29e 100644
--- a/include/linux/reset-controller.h
+++ b/include/linux/reset-controller.h
@@ -61,6 +61,7 @@ struct reset_control_lookup {
  * @dev: corresponding driver model device struct
  * @of_node: corresponding device tree node as phandle target
  * @of_reset_n_cells: number of cells in reset line specifiers
+ * @cookie: for reset-gpios controllers: corresponding GPIO instead of of_node
  * @of_xlate: translation function to translate from specifier as found in the
  *            device tree to id as given to the reset control ops, defaults
  *            to :c:func:`of_reset_simple_xlate`.
@@ -74,6 +75,7 @@ struct reset_controller_dev {
 	struct device *dev;
 	struct device_node *of_node;
 	int of_reset_n_cells;
+	const void *cookie;
 	int (*of_xlate)(struct reset_controller_dev *rcdev,
 			const struct of_phandle_args *reset_spec);
 	unsigned int nr_resets;
-- 
2.34.1