[PATCH v3 1/1] rtc: ds3232: get SRAM access using NVMEM Framework

[Han Nandor]

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@xxxxxxxxxxx>
---

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
`

Testing on Kernel v5.1.0-rc3

1. Update `arch/arm/configs/imx_v6_v7_defconfig` to contain
`CONFIG_RTC_DRV_DS3232=y`
2. Verify that building the kernel is successful: PASS
`
make ARCH=arm CROSS_COMPILE=arm-linux-gnu- imx_v6_v7_defconfig zImage
...
CC      drivers/rtc/rtc-ds3232.o
...
Kernel: arch/arm/boot/zImage is ready
`

Changes since v1
----------------
 - remove the unnecessary header "rtc-core.h"
 - use nvmem_config from the stack
 - configure the nvmem type
 - remove the `of_node` configuration

Changes since v2
----------------
 - init unused struct nvmem_cfg members to 0
 - use regmap as private data to nvmem struct

 drivers/rtc/rtc-ds3232.c | 40 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 38 insertions(+), 2 deletions(-)

diff --git a/drivers/rtc/rtc-ds3232.c b/drivers/rtc/rtc-ds3232.c
index 7184e5145f12..1e9312f96021 100644
--- a/drivers/rtc/rtc-ds3232.c
+++ b/drivers/rtc/rtc-ds3232.c
@@ -48,6 +48,10 @@
 #       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;
@@ -461,11 +465,39 @@ 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 regmap *ds3232_regmap = (struct regmap *)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 regmap *ds3232_regmap = (struct regmap *)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)
 {
 	struct ds3232 *ds3232;
 	int ret;
+	struct nvmem_config nvmem_cfg = {
+		.name = "ds3232_sram",
+		.stride = 1,
+		.size = DS3232_REG_SRAM_SIZE,
+		.word_size = 1,
+		.reg_read = ds3232_nvmem_read,
+		.reg_write = ds3232_nvmem_write,
+		.priv = regmap,
+		.type = NVMEM_TYPE_BATTERY_BACKED
+	};
 
 	ds3232 = devm_kzalloc(dev, sizeof(*ds3232), GFP_KERNEL);
 	if (!ds3232)
@@ -490,6 +522,10 @@ static int ds3232_probe(struct device *dev, struct regmap *regmap, int irq,
 	if (IS_ERR(ds3232->rtc))
 		return PTR_ERR(ds3232->rtc);
 
+	ret = rtc_nvmem_register(ds3232->rtc, &nvmem_cfg);
+	if(ret)
+		return ret;
+
 	if (ds3232->irq > 0) {
 		ret = devm_request_threaded_irq(dev, ds3232->irq, NULL,
 						ds3232_irq,
@@ -542,7 +578,7 @@ 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 +645,7 @@ 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