rtc: ds1390: Add trickle charger device tree binding

Introduce a device tree binding for specifying the trickle charger
configuration for ds1390.

Signed-off-by: Ivan Grimaldi <grimaldi.ivan@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

2 files changed, 65 insertions, 2 deletions

diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index 9d4290617cee..57c2dbc4f438 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -666,8 +666,8 @@ config RTC_DRV_DS1390
           If you say yes here you get support for the
           Dallas/Maxim DS1390/93/94 chips.
 
-          This driver only supports the RTC feature, and not other chip
-          features such as alarms and trickle charging.
+          This driver supports the RTC feature and trickle charging but not
+          other chip features such as alarms.
 
           This driver can also be built as a module. If so, the module
           will be called rtc-ds1390.
diff --git a/drivers/rtc/rtc-ds1390.c b/drivers/rtc/rtc-ds1390.c
index a4303b43a36a..b2b9454aa7a2 100644
--- a/drivers/rtc/rtc-ds1390.c
+++ b/drivers/rtc/rtc-ds1390.c
@@ -20,6 +20,7 @@
 #include <linux/spi/spi.h>
 #include <linux/bcd.h>
 #include <linux/slab.h>
+#include <linux/of.h>
 
 #define DS1390_REG_100THS               0x00
 #define DS1390_REG_SECONDS              0x01
@@ -40,11 +41,31 @@
 #define DS1390_REG_STATUS               0x0E
 #define DS1390_REG_TRICKLE              0x0F
 
+#define DS1390_TRICKLE_CHARGER_ENABLE   0xA0
+#define DS1390_TRICKLE_CHARGER_250_OHM  0x01
+#define DS1390_TRICKLE_CHARGER_2K_OHM   0x02
+#define DS1390_TRICKLE_CHARGER_4K_OHM   0x03
+#define DS1390_TRICKLE_CHARGER_NO_DIODE 0x04
+#define DS1390_TRICKLE_CHARGER_DIODE    0x08
+
 struct ds1390 {
         struct rtc_device *rtc;
         u8 txrx_buf[9]; /* cmd + 8 registers */
 };
 
+static void ds1390_set_reg(struct device *dev, unsigned char address,
+                           unsigned char data)
+{
+        struct spi_device *spi = to_spi_device(dev);
+        unsigned char buf[2];
+
+        /* MSB must be '1' to write */
+        buf[0] = address | 0x80;
+        buf[1] = data;
+
+        spi_write(spi, buf, 2);
+}
+
 static int ds1390_get_reg(struct device *dev, unsigned char address,
                                 unsigned char *data)
 {
@@ -67,6 +88,45 @@ static int ds1390_get_reg(struct device *dev, unsigned char address,
         return 0;
 }
 
+static void ds1390_trickle_of_init(struct spi_device *spi)
+{
+        u32 ohms = 0;
+        u8 value;
+
+        if (of_property_read_u32(spi->dev.of_node, "trickle-resistor-ohms",
+                                 &ohms))
+                goto out;
+
+        /* Enable charger */
+        value = DS1390_TRICKLE_CHARGER_ENABLE;
+        if (of_property_read_bool(spi->dev.of_node, "trickle-diode-disable"))
+                value |= DS1390_TRICKLE_CHARGER_NO_DIODE;
+        else
+                value |= DS1390_TRICKLE_CHARGER_DIODE;
+
+        /* Resistor select */
+        switch (ohms) {
+        case 250:
+                value |= DS1390_TRICKLE_CHARGER_250_OHM;
+                break;
+        case 2000:
+                value |= DS1390_TRICKLE_CHARGER_2K_OHM;
+                break;
+        case 4000:
+                value |= DS1390_TRICKLE_CHARGER_4K_OHM;
+                break;
+        default:
+                dev_warn(&spi->dev,
+                         "Unsupported ohm value %02ux in dt\n", ohms);
+                return;
+        }
+
+        ds1390_set_reg(&spi->dev, DS1390_REG_TRICKLE, value);
+
+out:
+        return;
+}
+
 static int ds1390_read_time(struct device *dev, struct rtc_time *dt)
 {
         struct spi_device *spi = to_spi_device(dev);
@@ -143,6 +203,9 @@ static int ds1390_probe(struct spi_device *spi)
                 return res;
         }
 
+        if (spi->dev.of_node)
+                ds1390_trickle_of_init(spi);
+
         chip->rtc = devm_rtc_device_register(&spi->dev, "ds1390",
                                         &ds1390_rtc_ops, THIS_MODULE);
         if (IS_ERR(chip->rtc)) {