1 files changed, 81 insertions, 5 deletions

diff --git a/drivers/rtc/rtc-mcp795.c b/drivers/rtc/rtc-mcp795.c
index 4618f4fa655f..89b0ffa83064 100644
--- a/drivers/rtc/rtc-mcp795.c
+++ b/drivers/rtc/rtc-mcp795.c
@@ -22,6 +22,7 @@
 #include <linux/rtc.h>
 #include <linux/of.h>
 #include <linux/bcd.h>
+#include <linux/delay.h>
 
 /* MCP795 Instructions, see datasheet table 3-1 */
 #define MCP795_EEREAD   0x03
@@ -38,9 +39,17 @@
 #define MCP795_CLRWDT   0x44
 #define MCP795_CLRRAM   0x54
 
+/* MCP795 RTCC registers, see datasheet table 4-1 */
+#define MCP795_REG_SECONDS      0x01
+#define MCP795_REG_DAY          0x04
+#define MCP795_REG_MONTH        0x06
+#define MCP795_REG_CONTROL      0x08
+
 #define MCP795_ST_BIT   0x80
 #define MCP795_24_BIT   0x40
 #define MCP795_LP_BIT   BIT(5)
+#define MCP795_EXTOSC_BIT       BIT(3)
+#define MCP795_OSCON_BIT        BIT(5)
 
 static int mcp795_rtcc_read(struct device *dev, u8 addr, u8 *buf, u8 count)
 {
@@ -95,13 +104,65 @@ static int mcp795_rtcc_set_bits(struct device *dev, u8 addr, u8 mask, u8 state)
         return ret;
 }
 
+static int mcp795_stop_oscillator(struct device *dev, bool *extosc)
+{
+        int retries = 5;
+        int ret;
+        u8 data;
+
+        ret = mcp795_rtcc_set_bits(dev, MCP795_REG_SECONDS, MCP795_ST_BIT, 0);
+        if (ret)
+                return ret;
+        ret = mcp795_rtcc_read(dev, MCP795_REG_CONTROL, &data, 1);
+        if (ret)
+                return ret;
+        *extosc = !!(data & MCP795_EXTOSC_BIT);
+        ret = mcp795_rtcc_set_bits(
+                                dev, MCP795_REG_CONTROL, MCP795_EXTOSC_BIT, 0);
+        if (ret)
+                return ret;
+        /* wait for the OSCON bit to clear */
+        do {
+                usleep_range(700, 800);
+                ret = mcp795_rtcc_read(dev, MCP795_REG_DAY, &data, 1);
+                if (ret)
+                        break;
+                if (!(data & MCP795_OSCON_BIT))
+                        break;
+
+        } while (--retries);
+
+        return !retries ? -EIO : ret;
+}
+
+static int mcp795_start_oscillator(struct device *dev, bool *extosc)
+{
+        if (extosc) {
+                u8 data = *extosc ? MCP795_EXTOSC_BIT : 0;
+                int ret;
+
+                ret = mcp795_rtcc_set_bits(
+                        dev, MCP795_REG_CONTROL, MCP795_EXTOSC_BIT, data);
+                if (ret)
+                        return ret;
+        }
+        return mcp795_rtcc_set_bits(
+                        dev, MCP795_REG_SECONDS, MCP795_ST_BIT, MCP795_ST_BIT);
+}
+
 static int mcp795_set_time(struct device *dev, struct rtc_time *tim)
 {
         int ret;
         u8 data[7];
+        bool extosc;
+
+        /* Stop RTC and store current value of EXTOSC bit */
+        ret = mcp795_stop_oscillator(dev, &extosc);
+        if (ret)
+                return ret;
 
         /* Read first, so we can leave config bits untouched */
-        ret = mcp795_rtcc_read(dev, 0x01, data, sizeof(data));
+        ret = mcp795_rtcc_read(dev, MCP795_REG_SECONDS, data, sizeof(data));
 
         if (ret)
                 return ret;
@@ -117,8 +178,23 @@ static int mcp795_set_time(struct device *dev, struct rtc_time *tim)
 
         data[6] = bin2bcd(tim->tm_year);
 
-        ret = mcp795_rtcc_write(dev, 0x01, data, sizeof(data));
+        /* Always write the date and month using a separate Write command.
+         * This is a workaround for a know silicon issue that some combinations
+         * of date and month values may result in the date being reset to 1.
+         */
+        ret = mcp795_rtcc_write(dev, MCP795_REG_SECONDS, data, 5);
+        if (ret)
+                return ret;
+
+        ret = mcp795_rtcc_write(dev, MCP795_REG_MONTH, &data[5], 2);
+        if (ret)
+                return ret;
 
+        /* Start back RTC and restore previous value of EXTOSC bit.
+         * There is no need to clear EXTOSC bit when the previous value was 0
+         * because it was already cleared when stopping the RTC oscillator.
+         */
+        ret = mcp795_start_oscillator(dev, extosc ? &extosc : NULL);
         if (ret)
                 return ret;
 
@@ -134,7 +210,7 @@ static int mcp795_read_time(struct device *dev, struct rtc_time *tim)
         int ret;
         u8 data[7];
 
-        ret = mcp795_rtcc_read(dev, 0x01, data, sizeof(data));
+        ret = mcp795_rtcc_read(dev, MCP795_REG_SECONDS, data, sizeof(data));
 
         if (ret)
                 return ret;
@@ -171,8 +247,8 @@ static int mcp795_probe(struct spi_device *spi)
                 return ret;
         }
 
-        /* Start the oscillator */
-        mcp795_rtcc_set_bits(&spi->dev, 0x01, MCP795_ST_BIT, MCP795_ST_BIT);
+        /* Start the oscillator but don't set the value of EXTOSC bit */
+        mcp795_start_oscillator(&spi->dev, NULL);
         /* Clear the 12 hour mode flag*/
         mcp795_rtcc_set_bits(&spi->dev, 0x03, MCP795_24_BIT, 0);