[PATCH v1 07/15] pwrseq: add fallback support

[Dmitry Baryshkov]

Power sequencer support requires changing device tree. To ease migration
to pwrseq, add support for pwrseq 'fallback': let the power sequencer
driver register special handler that if matched will create pwrseq
instance basing on the consumer device tree data.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov at linaro.org>
---
 drivers/power/pwrseq/Makefile   |  2 +-
 drivers/power/pwrseq/core.c     |  3 ++
 drivers/power/pwrseq/fallback.c | 88 +++++++++++++++++++++++++++++++++
 include/linux/pwrseq/fallback.h | 60 ++++++++++++++++++++++
 4 files changed, 152 insertions(+), 1 deletion(-)
 create mode 100644 drivers/power/pwrseq/fallback.c
 create mode 100644 include/linux/pwrseq/fallback.h

diff --git a/drivers/power/pwrseq/Makefile b/drivers/power/pwrseq/Makefile
index 556bf5582d47..949ec848cf00 100644
--- a/drivers/power/pwrseq/Makefile
+++ b/drivers/power/pwrseq/Makefile
@@ -3,7 +3,7 @@
 # Makefile for power sequencer drivers.
 #
 
-obj-$(CONFIG_PWRSEQ) += core.o
+obj-$(CONFIG_PWRSEQ) += core.o fallback.o
 
 obj-$(CONFIG_PWRSEQ_EMMC)	+= pwrseq_emmc.o
 obj-$(CONFIG_PWRSEQ_QCA)	+= pwrseq_qca.o
diff --git a/drivers/power/pwrseq/core.c b/drivers/power/pwrseq/core.c
index 3dffa52f65ee..30380ca6159a 100644
--- a/drivers/power/pwrseq/core.c
+++ b/drivers/power/pwrseq/core.c
@@ -14,6 +14,7 @@
 #include <linux/of.h>
 #include <linux/pwrseq/consumer.h>
 #include <linux/pwrseq/driver.h>
+#include <linux/pwrseq/fallback.h>
 #include <linux/slab.h>
 
 #define	to_pwrseq(a)	(container_of((a), struct pwrseq, dev))
@@ -120,6 +121,8 @@ struct pwrseq * pwrseq_get(struct device *dev, const char *id)
 	struct pwrseq *pwrseq;
 
 	pwrseq = _of_pwrseq_get(dev, id);
+	if (pwrseq == NULL)
+		pwrseq = pwrseq_fallback_get(dev, id);
 	if (IS_ERR_OR_NULL(pwrseq))
 		return pwrseq;
 
diff --git a/drivers/power/pwrseq/fallback.c b/drivers/power/pwrseq/fallback.c
new file mode 100644
index 000000000000..b83bd5795ccb
--- /dev/null
+++ b/drivers/power/pwrseq/fallback.c
@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2021 (c) Linaro Ltd.
+ * Author: Dmitry Baryshkov <dmitry.baryshkov at linaro.org>
+ */
+
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/of_device.h>
+#include <linux/pwrseq/fallback.h>
+#include <linux/slab.h>
+
+static DEFINE_MUTEX(pwrseq_fallback_mutex);
+static LIST_HEAD(pwrseq_fallback_list);
+
+/**
+ * __pwrseq_fallback_register - internal helper for pwrseq_fallback_register
+ * @fallback - struct pwrseq_fallback to be registered
+ * @owner: module containing fallback callback
+ *
+ * Internal helper for pwrseq_fallback_register. It should not be called directly.
+ */
+int __pwrseq_fallback_register(struct pwrseq_fallback *fallback, struct module *owner)
+{
+	if (!try_module_get(owner))
+		return -EPROBE_DEFER;
+
+	fallback->owner = owner;
+
+	mutex_lock(&pwrseq_fallback_mutex);
+	list_add_tail(&fallback->list, &pwrseq_fallback_list);
+	mutex_unlock(&pwrseq_fallback_mutex);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(__pwrseq_fallback_register);
+
+/**
+ * pwrseq_fallback_unregister() - unregister fallback helper
+ * @fallback - struct pwrseq_fallback to unregister
+ *
+ * Unregister pwrseq fallback handler registered by pwrseq_fallback_handler.
+ */
+void pwrseq_fallback_unregister(struct pwrseq_fallback *fallback)
+{
+	mutex_lock(&pwrseq_fallback_mutex);
+	list_del(&fallback->list);
+	mutex_unlock(&pwrseq_fallback_mutex);
+
+	module_put(fallback->owner);
+
+	kfree(fallback);
+}
+EXPORT_SYMBOL_GPL(pwrseq_fallback_unregister);
+
+static bool pwrseq_fallback_match(struct device *dev, struct pwrseq_fallback *fallback)
+{
+	if (of_match_device(fallback->of_match_table, dev) != NULL)
+		return true;
+
+	/* We might add support for other matching options later */
+
+	return false;
+}
+
+struct pwrseq *pwrseq_fallback_get(struct device *dev, const char *id)
+{
+	struct pwrseq_fallback *fallback;
+	struct pwrseq *pwrseq = ERR_PTR(-ENODEV);
+
+	mutex_lock(&pwrseq_fallback_mutex);
+
+	list_for_each_entry(fallback, &pwrseq_fallback_list, list) {
+		if (!pwrseq_fallback_match(dev, fallback))
+			continue;
+
+		pwrseq = fallback->get(dev, id);
+		break;
+	}
+
+	mutex_unlock(&pwrseq_fallback_mutex);
+
+	if (!IS_ERR_OR_NULL(pwrseq))
+		dev_warn(dev, "legacy pwrseq support used for the device\n");
+
+	return pwrseq;
+}
diff --git a/include/linux/pwrseq/fallback.h b/include/linux/pwrseq/fallback.h
new file mode 100644
index 000000000000..14f9aa527692
--- /dev/null
+++ b/include/linux/pwrseq/fallback.h
@@ -0,0 +1,60 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (c) 2021 Linaro Ltd.
+ */
+
+#ifndef __LINUX_PWRSEQ_FALLBACK_H__
+#define __LINUX_PWRSEQ_FALLBACK_H__
+
+#include <linux/list.h>
+
+struct pwrseq;
+
+struct device;
+struct module;
+struct of_device_id;
+
+/**
+ * struct pwrseq_fallback - structure providing fallback data/
+ * @list: a list node for the fallback handlers
+ * @owner: module containing fallback callback
+ * @of_match_table: match table for this fallback
+ *
+ * Pwrseq fallback is a mechanism for handling backwards compatibility in the
+ * case device tree was not updated to use proper pwrseq providers.
+ *
+ * In case the pwrseq instance is not registered, core will automatically try
+ * locating and calling fallback getter. If the requesting device matches
+ * against @of_match_table, the @get callback will be called to retrieve pwrseq
+ * instance.
+ *
+ * The driver should fill of_match_table and @get fields only. @list and @owner
+ * will be filled by the core code.
+ */
+struct pwrseq_fallback {
+	struct list_head list;
+	struct module *owner;
+
+	const struct of_device_id *of_match_table;
+
+	struct pwrseq *(*get)(struct device *dev, const char *id);
+};
+
+/* provider interface */
+
+int __pwrseq_fallback_register(struct pwrseq_fallback *fallback, struct module *owner);
+
+/**
+ * pwrseq_fallback_register() - register fallback helper
+ * @fallback - struct pwrseq_fallback to be registered
+ *
+ * Register pwrseq fallback handler to assist pwrseq core.
+ */
+#define pwrseq_fallback_register(fallback) __pwrseq_fallback_register(fallback, THIS_MODULE)
+
+void pwrseq_fallback_unregister(struct pwrseq_fallback *fallback);
+
+/* internal interface to be used by pwrseq core */
+struct pwrseq *pwrseq_fallback_get(struct device *dev, const char *id);
+
+#endif /* __LINUX_PWRSEQ_DRIVER_H__ */
-- 
2.33.0