rtc: pcf2127: add support for accessing internal static RAM

The PCF2127 has 512 bytes of internal static RAM and this patch expands
the driver to access this memory.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-pcf2127.c

@@ -36,6 +36,11 @@
 #define PCF2127_REG_MO          (0x08)
 #define PCF2127_REG_YR          (0x09)
 
+/* the pcf2127 has 512 bytes nvmem, pcf2129 doesn't */
+#define PCF2127_REG_RAM_addr_MSB       0x1a
+#define PCF2127_REG_RAM_wrt_cmd        0x1c
+#define PCF2127_REG_RAM_rd_cmd         0x1d
+
 #define PCF2127_OSF             BIT(7)  /* Oscillator Fail flag */
 
 struct pcf2127 {
@@ -183,10 +188,47 @@ static const struct rtc_class_ops pcf2127_rtc_ops = {
 	.set_time	= pcf2127_rtc_set_time,
 };
 
+static int pcf2127_nvmem_read(void *priv, unsigned int offset,
+			      void *val, size_t bytes)
+{
+	struct pcf2127 *pcf2127 = priv;
+	int ret;
+	unsigned char offsetbuf[] = { offset >> 8, offset };
+
+	ret = regmap_bulk_write(pcf2127->regmap, PCF2127_REG_RAM_addr_MSB,
+				offsetbuf, 2);
+	if (ret)
+		return ret;
+
+	ret = regmap_bulk_read(pcf2127->regmap, PCF2127_REG_RAM_rd_cmd,
+			       val, bytes);
+
+	return ret ?: bytes;
+}
+
+static int pcf2127_nvmem_write(void *priv, unsigned int offset,
+			       void *val, size_t bytes)
+{
+	struct pcf2127 *pcf2127 = priv;
+	int ret;
+	unsigned char offsetbuf[] = { offset >> 8, offset };
+
+	ret = regmap_bulk_write(pcf2127->regmap, PCF2127_REG_RAM_addr_MSB,
+				offsetbuf, 2);
+	if (ret)
+		return ret;
+
+	ret = regmap_bulk_write(pcf2127->regmap, PCF2127_REG_RAM_wrt_cmd,
+				val, bytes);
+
+	return ret ?: bytes;
+}
+
 static int pcf2127_probe(struct device *dev, struct regmap *regmap,
-			const char *name)
+			const char *name, bool has_nvmem)
 {
 	struct pcf2127 *pcf2127;
+	int ret = 0;
 
 	dev_dbg(dev, "%s\n", __func__);
 
@@ -200,8 +242,21 @@ static int pcf2127_probe(struct device *dev, struct regmap *regmap,
 
 	pcf2127->rtc = devm_rtc_device_register(dev, name, &pcf2127_rtc_ops,
 						THIS_MODULE);
+	if (IS_ERR(pcf2127->rtc))
+		return PTR_ERR(pcf2127->rtc);
+
+	if (has_nvmem) {
+		struct nvmem_config nvmem_cfg = {
+			.priv = pcf2127,
+			.reg_read = pcf2127_nvmem_read,
+			.reg_write = pcf2127_nvmem_write,
+			.size = 512,
+		};
+
+		ret = rtc_nvmem_register(pcf2127->rtc, &nvmem_cfg);
+	}
 
-	return PTR_ERR_OR_ZERO(pcf2127->rtc);
+	return ret;
 }
 
 #ifdef CONFIG_OF
@@ -309,11 +364,11 @@ static int pcf2127_i2c_probe(struct i2c_client *client,
 	}
 
 	return pcf2127_probe(&client->dev, regmap,
-				pcf2127_i2c_driver.driver.name);
+			     pcf2127_i2c_driver.driver.name, id->driver_data);
 }
 
 static const struct i2c_device_id pcf2127_i2c_id[] = {
-	{ "pcf2127", 0 },
+	{ "pcf2127", 1 },
 	{ "pcf2129", 0 },
 	{ }
 };
@@ -372,11 +427,12 @@ static int pcf2127_spi_probe(struct spi_device *spi)
 		return PTR_ERR(regmap);
 	}
 
-	return pcf2127_probe(&spi->dev, regmap, pcf2127_spi_driver.driver.name);
+	return pcf2127_probe(&spi->dev, regmap, pcf2127_spi_driver.driver.name,
+			     spi_get_device_id(spi)->driver_data);
 }
 
 static const struct spi_device_id pcf2127_spi_id[] = {
-	{ "pcf2127", 0 },
+	{ "pcf2127", 1 },
 	{ "pcf2129", 0 },
 	{ }
 };