[PATCH 1/1] rtc: ds3232: get SRAM access using NVMEM Framework

[Han Nandor <nandor.han@vaisala.com>]

DS3232 RTC has 236 bytes of persistent memory.

Add RTC SRAM read and write access using
the NVMEM Framework.

Signed-off-by: Nandor Han <nandor.han@vaisala.com>
---

Description
-----------
Provides DS3232 RTC SRAM access using NVMEM framework.

Testing
-------
The test was done on a custom board which contains a
DS3232 RTC device.
Kernel Version: 4.14.60 (Just for clarity, the patch is against master)

1. Verify that SRAM is accessible using NVMEM interface: PASS
`
# hexdump /sys/bus/nvmem/devices/ds3232_sram0/nvmem
0000000 0000 0000 0000 0000 0000 0000 0000 0000
*
00000e0
`
2. Modify the content.
`
# echo testing > /sys/bus/nvmem/devices/ds3232_sram0/nvmem
#
`
3. Power cycle the board and verify that contents are preserved: PASS
`
# hexdump -n 10 -C /sys/bus/nvmem/devices/ds3232_sram0/nvmem
00000000  74 65 73 74 69 6e 67 0a  00 00                    |testing...|
0000000a
`

 drivers/rtc/rtc-ds3232.c | 41 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 39 insertions(+), 2 deletions(-)

diff --git a/drivers/rtc/rtc-ds3232.c b/drivers/rtc/rtc-ds3232.c
index 7184e5145f12..fe615aedaa9a 100644
--- a/drivers/rtc/rtc-ds3232.c
+++ b/drivers/rtc/rtc-ds3232.c
@@ -24,6 +24,8 @@
 #include <linux/regmap.h>
 #include <linux/hwmon.h>
 
+#include "rtc-core.h"
+
 #define DS3232_REG_SECONDS      0x00
 #define DS3232_REG_MINUTES      0x01
 #define DS3232_REG_HOURS        0x02
@@ -48,12 +50,17 @@
 #       define DS3232_REG_SR_A1F     0x01
 
 #define DS3232_REG_TEMPERATURE	0x11
+#define DS3232_REG_SRAM_START   0x14
+#define DS3232_REG_SRAM_END     0xFF
+
+#define DS3232_REG_SRAM_SIZE    236
 
 struct ds3232 {
 	struct device *dev;
 	struct regmap *regmap;
 	int irq;
 	struct rtc_device *rtc;
+	struct nvmem_config	nvmem_cfg;
 
 	bool suspended;
 };
@@ -461,6 +468,24 @@ static const struct rtc_class_ops ds3232_rtc_ops = {
 	.alarm_irq_enable = ds3232_alarm_irq_enable,
 };
 
+static int ds3232_nvmem_read(void *priv, unsigned int offset, void *val,
+			     size_t bytes)
+{
+	struct ds3232 *ds3232 = (struct ds3232 *)priv;
+
+	return regmap_bulk_read(ds3232->regmap, DS3232_REG_SRAM_START + offset,
+				val, bytes);
+}
+
+static int ds3232_nvmem_write(void *priv, unsigned int offset, void *val,
+			      size_t bytes)
+{
+	struct ds3232 *ds3232 = (struct ds3232 *)priv;
+
+	return regmap_bulk_write(ds3232->regmap, DS3232_REG_SRAM_START + offset,
+				 val, bytes);
+}
+
 static int ds3232_probe(struct device *dev, struct regmap *regmap, int irq,
 			const char *name)
 {
@@ -476,6 +501,14 @@ static int ds3232_probe(struct device *dev, struct regmap *regmap, int irq,
 	ds3232->dev = dev;
 	dev_set_drvdata(dev, ds3232);
 
+	ds3232->nvmem_cfg.name = "ds3232_sram";
+	ds3232->nvmem_cfg.stride = 1;
+	ds3232->nvmem_cfg.size = DS3232_REG_SRAM_SIZE;
+	ds3232->nvmem_cfg.word_size = 1;
+	ds3232->nvmem_cfg.reg_read = ds3232_nvmem_read;
+	ds3232->nvmem_cfg.reg_write = ds3232_nvmem_write;
+	ds3232->nvmem_cfg.priv = ds3232;
+
 	ret = ds3232_check_rtc_status(dev);
 	if (ret)
 		return ret;
@@ -490,6 +523,10 @@ static int ds3232_probe(struct device *dev, struct regmap *regmap, int irq,
 	if (IS_ERR(ds3232->rtc))
 		return PTR_ERR(ds3232->rtc);
 
+	ds3232->rtc->dev.of_node = dev->of_node;
+	ds3232->rtc->nvmem_config = &ds3232->nvmem_cfg;
+	rtc_nvmem_register(ds3232->rtc);
+
 	if (ds3232->irq > 0) {
 		ret = devm_request_threaded_irq(dev, ds3232->irq, NULL,
 						ds3232_irq,
@@ -542,7 +579,7 @@ static int ds3232_i2c_probe(struct i2c_client *client,
 	static const struct regmap_config config = {
 		.reg_bits = 8,
 		.val_bits = 8,
-		.max_register = 0x13,
+		.max_register = DS3232_REG_SRAM_END,
 	};
 
 	regmap = devm_regmap_init_i2c(client, &config);
@@ -609,7 +646,7 @@ static int ds3234_probe(struct spi_device *spi)
 	static const struct regmap_config config = {
 		.reg_bits = 8,
 		.val_bits = 8,
-		.max_register = 0x13,
+		.max_register = DS3232_REG_SRAM_END,
 		.write_flag_mask = 0x80,
 	};
 	struct regmap *regmap;
-- 
2.17.2