summaryrefslogtreecommitdiffstats
path: root/drivers
diff options
context:
space:
mode:
authorEmil Bartczak <emilbart@gmail.com>2016-12-08 00:27:40 +0100
committerAlexandre Belloni <alexandre.belloni@free-electrons.com>2016-12-19 00:59:23 +0100
commit43d0b10f60c54667108729adb525bc1090d4238f (patch)
tree3e47d6827ebbb32f5de50893c7b91071457251db /drivers
parent26eeefd5956449b03c87c49b996e012ffe3e59aa (diff)
downloadlinux-43d0b10f60c54667108729adb525bc1090d4238f.tar.bz2
rtc: mcp795: fix month write resetting date to 1.
According to Microchip errata some combinations of date and month values may result in the date being reset to 1, even if the date is also written with the month (for example 31-07 or 31-08). As a workaround avoid writing date and month values within the same Write command. Instead, terminate the Write command after loading the date and begin a new command to write the month. In addition, disable the oscillator before loading the new values. This is done by ensuring both the ST and EXTOSC bits are cleared and waiting for the OSCON bit to clear. Signed-off-by: Emil Bartczak <emilbart@gmail.com> Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/rtc/rtc-mcp795.c86
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);