rtc: isl1208: Add new style nvmem support to driver

Add support for the RTC's NVRAM using the standard nvmem support that is
part of the Linux RTC framework.

This driver already has a sysfs attribute that provides access to the
RTC's NVRAM as a single 16-bit value.  Some chips have more than two
bytes of NVRAM, so this will not work for them.  It's also non-standard.

This sysfs attribute is left in for backward compatibility, but will only
be able to read the first two bytes of NVRAM.  The nvmem interface will
allow access to all NVRAM, e.g. eight bytes on the isl1218.

Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Trent Piepho <tpiepho@impinj.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-isl1208.c

@@ -115,6 +115,7 @@ MODULE_DEVICE_TABLE(of, isl1208_of_match);
 
 /* Device state */
 struct isl1208_state {
+	struct nvmem_config nvmem_config;
 	struct rtc_device *rtc;
 	const struct isl1208_config *config;
 };
@@ -742,6 +743,46 @@ static const struct attribute_group isl1219_rtc_sysfs_files = {
 	.attrs	= isl1219_rtc_attrs,
 };
 
+static int isl1208_nvmem_read(void *priv, unsigned int off, void *buf,
+			      size_t count)
+{
+	struct isl1208_state *isl1208 = priv;
+	struct i2c_client *client = to_i2c_client(isl1208->rtc->dev.parent);
+	int ret;
+
+	/* nvmem sanitizes offset/count for us, but count==0 is possible */
+	if (!count)
+		return count;
+	ret = isl1208_i2c_read_regs(client, ISL1208_REG_USR1 + off, buf,
+				    count);
+	return ret == 0 ? count : ret;
+}
+
+static int isl1208_nvmem_write(void *priv, unsigned int off, void *buf,
+			       size_t count)
+{
+	struct isl1208_state *isl1208 = priv;
+	struct i2c_client *client = to_i2c_client(isl1208->rtc->dev.parent);
+	int ret;
+
+	/* nvmem sanitizes off/count for us, but count==0 is possible */
+	if (!count)
+		return count;
+	ret = isl1208_i2c_set_regs(client, ISL1208_REG_USR1 + off, buf,
+				   count);
+
+	return ret == 0 ? count : ret;
+}
+
+static const struct nvmem_config isl1208_nvmem_config = {
+	.name = "isl1208_nvram",
+	.word_size = 1,
+	.stride = 1,
+	/* .size from chip specific config */
+	.reg_read = isl1208_nvmem_read,
+	.reg_write = isl1208_nvmem_write,
+};
+
 static int isl1208_setup_irq(struct i2c_client *client, int irq)
 {
 	int rc = devm_request_threaded_irq(&client->dev, irq, NULL,
@@ -796,6 +837,11 @@ isl1208_probe(struct i2c_client *client, const struct i2c_device_id *id)
 
 	isl1208->rtc->ops = &isl1208_rtc_ops;
 
+	/* Setup nvmem configuration in driver state struct */
+	isl1208->nvmem_config = isl1208_nvmem_config;
+	isl1208->nvmem_config.size = isl1208->config->nvmem_length;
+	isl1208->nvmem_config.priv = isl1208;
+
 	rc = isl1208_i2c_get_sr(client);
 	if (rc < 0) {
 		dev_err(&client->dev, "reading status failed\n");
@@ -849,6 +895,10 @@ isl1208_probe(struct i2c_client *client, const struct i2c_device_id *id)
 	if (rc)
 		return rc;
 
+	rc = rtc_nvmem_register(isl1208->rtc, &isl1208->nvmem_config);
+	if (rc)
+		return rc;
+
 	return rtc_register_device(isl1208->rtc);
 }