rtc: add generic nvmem support

Many RTCs have an on board non volatile storage. It can be battery backed
RAM or an EEPROM. Use the nvmem subsystem to export it to both userspace
and in-kernel consumers.

This stays compatible with the previous (non documented) ABI that was using
/sys/class/rtc/rtcx/device/nvram to export that memory. But will warn about
the deprecation.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

5 files changed, 134 insertions, 0 deletions

diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index d0e4b4a1c2a1..72419ac2c52a 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -77,6 +77,14 @@ config RTC_DEBUG
 	  Say yes here to enable debugging support in the RTC framework
 	  and individual RTC drivers.
 
+config RTC_NVMEM
+	bool "RTC non volatile storage support"
+	select NVMEM
+	default RTC_CLASS
+	help
+	  Say yes here to add support for the non volatile (often battery
+	  backed) storage present on RTCs.
+
 comment "RTC interfaces"
 
 config RTC_INTF_SYSFS
diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
index 4050fc8b9271..acd366b41c85 100644
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -15,6 +15,7 @@ ifdef CONFIG_RTC_DRV_EFI
 rtc-core-y			+= rtc-efi-platform.o
 endif
 
+rtc-core-$(CONFIG_RTC_NVMEM)		+= nvmem.o
 rtc-core-$(CONFIG_RTC_INTF_DEV)		+= rtc-dev.o
 rtc-core-$(CONFIG_RTC_INTF_PROC)	+= rtc-proc.o
 rtc-core-$(CONFIG_RTC_INTF_SYSFS)	+= rtc-sysfs.o
diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
index 58e2a05765bb..2ed970d61da1 100644
--- a/drivers/rtc/class.c
+++ b/drivers/rtc/class.c
@@ -290,6 +290,8 @@ EXPORT_SYMBOL_GPL(rtc_device_register);
  */
 void rtc_device_unregister(struct rtc_device *rtc)
 {
+	rtc_nvmem_unregister(rtc);
+
 	mutex_lock(&rtc->ops_lock);
 	/*
 	 * Remove innards of this RTC, then disable it, before
@@ -448,6 +450,8 @@ int __rtc_register_device(struct module *owner, struct rtc_device *rtc)
 
 	rtc_proc_add_device(rtc);
 
+	rtc_nvmem_register(rtc);
+
 	rtc->registered = true;
 	dev_info(rtc->dev.parent, "registered as %s\n",
 		 dev_name(&rtc->dev));
diff --git a/drivers/rtc/nvmem.c b/drivers/rtc/nvmem.c
new file mode 100644
index 000000000000..8567b4ed9ac6
--- /dev/null
+++ b/drivers/rtc/nvmem.c
@@ -0,0 +1,113 @@
+/*
+ * RTC subsystem, nvmem interface
+ *
+ * Copyright (C) 2017 Alexandre Belloni
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/err.h>
+#include <linux/types.h>
+#include <linux/nvmem-consumer.h>
+#include <linux/rtc.h>
+#include <linux/sysfs.h>
+
+#include "rtc-core.h"
+
+/*
+ * Deprecated ABI compatibility, this should be removed at some point
+ */
+
+static const char nvram_warning[] = "Deprecated ABI, please use nvmem";
+
+static ssize_t
+rtc_nvram_read(struct file *filp, struct kobject *kobj,
+	       struct bin_attribute *attr,
+	       char *buf, loff_t off, size_t count)
+{
+	struct rtc_device *rtc = attr->private;
+
+	dev_warn_once(kobj_to_dev(kobj), nvram_warning);
+
+	return nvmem_device_read(rtc->nvmem, off, count, buf);
+}
+
+static ssize_t
+rtc_nvram_write(struct file *filp, struct kobject *kobj,
+		struct bin_attribute *attr,
+		char *buf, loff_t off, size_t count)
+{
+	struct rtc_device *rtc = attr->private;
+
+	dev_warn_once(kobj_to_dev(kobj), nvram_warning);
+
+	return nvmem_device_write(rtc->nvmem, off, count, buf);
+}
+
+static int rtc_nvram_register(struct rtc_device *rtc)
+{
+	int err;
+
+	rtc->nvram = devm_kzalloc(rtc->dev.parent,
+				sizeof(struct bin_attribute),
+				GFP_KERNEL);
+	if (!rtc->nvram)
+		return -ENOMEM;
+
+	rtc->nvram->attr.name = "nvram";
+	rtc->nvram->attr.mode = 0644;
+	rtc->nvram->private = rtc;
+
+	sysfs_bin_attr_init(rtc->nvram);
+
+	rtc->nvram->read = rtc_nvram_read;
+	rtc->nvram->write = rtc_nvram_write;
+	rtc->nvram->size = rtc->nvmem_config->size;
+
+	err = sysfs_create_bin_file(&rtc->dev.parent->kobj,
+				    rtc->nvram);
+	if (err) {
+		devm_kfree(rtc->dev.parent, rtc->nvram);
+		rtc->nvram = NULL;
+	}
+
+	return err;
+}
+
+static void rtc_nvram_unregister(struct rtc_device *rtc)
+{
+	sysfs_remove_bin_file(&rtc->dev.parent->kobj, rtc->nvram);
+}
+
+/*
+ * New ABI, uses nvmem
+ */
+void rtc_nvmem_register(struct rtc_device *rtc)
+{
+	if (!rtc->nvmem_config)
+		return;
+
+	rtc->nvmem_config->dev = &rtc->dev;
+	rtc->nvmem_config->owner = rtc->owner;
+	rtc->nvmem = nvmem_register(rtc->nvmem_config);
+	if (IS_ERR_OR_NULL(rtc->nvmem))
+		return;
+
+	/* Register the old ABI */
+	if (rtc->nvram_old_abi)
+		rtc_nvram_register(rtc);
+}
+
+void rtc_nvmem_unregister(struct rtc_device *rtc)
+{
+	if (IS_ERR_OR_NULL(rtc->nvmem))
+		return;
+
+	/* unregister the old ABI */
+	if (rtc->nvram)
+		rtc_nvram_unregister(rtc);
+
+	nvmem_unregister(rtc->nvmem);
+}
diff --git a/drivers/rtc/rtc-core.h b/drivers/rtc/rtc-core.h
index 7a4ed2f7c7d7..ecab76a3207c 100644
--- a/drivers/rtc/rtc-core.h
+++ b/drivers/rtc/rtc-core.h
@@ -45,3 +45,11 @@ static inline const struct attribute_group **rtc_get_dev_attribute_groups(void)
 	return NULL;
 }
 #endif
+
+#ifdef CONFIG_RTC_NVMEM
+void rtc_nvmem_register(struct rtc_device *rtc);
+void rtc_nvmem_unregister(struct rtc_device *rtc);
+#else
+static inline void rtc_nvmem_register(struct rtc_device *rtc) {}
+static inline void rtc_nvmem_unregister(struct rtc_device *rtc) {}
+#endif