rtc/ab8500: add calibration attribute to AB8500 RTC

The rtc_calibration attribute allows user-space to get and set the
AB8500's RtcCalibration register.  The AB8500 will then use the value in
this register to compensate for RTC drift every 60 seconds.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Mark Godfrey <mark.godfrey@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 112 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-ab8500.c b/drivers/rtc/rtc-ab8500.c
index 919b2e5cb7f..df7bfc304c5 100644
--- a/drivers/rtc/rtc-ab8500.c
+++ b/drivers/rtc/rtc-ab8500.c
@@ -258,6 +258,109 @@ static int ab8500_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alarm)
         return ab8500_rtc_irq_enable(dev, alarm->enabled);
 }
 
+
+static int ab8500_rtc_set_calibration(struct device *dev, int calibration)
+{
+        int retval;
+        u8  rtccal = 0;
+
+        /*
+         * Check that the calibration value (which is in units of 0.5
+         * parts-per-million) is in the AB8500's range for RtcCalibration
+         * register. -128 (0x80) is not permitted because the AB8500 uses
+         * a sign-bit rather than two's complement, so 0x80 is just another
+         * representation of zero.
+         */
+        if ((calibration < -127) || (calibration > 127)) {
+                dev_err(dev, "RtcCalibration value outside permitted range\n");
+                return -EINVAL;
+        }
+
+        /*
+         * The AB8500 uses sign (in bit7) and magnitude (in bits0-7)
+         * so need to convert to this sort of representation before writing
+         * into RtcCalibration register...
+         */
+        if (calibration >= 0)
+                rtccal = 0x7F & calibration;
+        else
+                rtccal = ~(calibration - 1) | 0x80;
+
+        retval = abx500_set_register_interruptible(dev, AB8500_RTC,
+                        AB8500_RTC_CALIB_REG, rtccal);
+
+        return retval;
+}
+
+static int ab8500_rtc_get_calibration(struct device *dev, int *calibration)
+{
+        int retval;
+        u8  rtccal = 0;
+
+        retval =  abx500_get_register_interruptible(dev, AB8500_RTC,
+                        AB8500_RTC_CALIB_REG, &rtccal);
+        if (retval >= 0) {
+                /*
+                 * The AB8500 uses sign (in bit7) and magnitude (in bits0-7)
+                 * so need to convert value from RtcCalibration register into
+                 * a two's complement signed value...
+                 */
+                if (rtccal & 0x80)
+                        *calibration = 0 - (rtccal & 0x7F);
+                else
+                        *calibration = 0x7F & rtccal;
+        }
+
+        return retval;
+}
+
+static ssize_t ab8500_sysfs_store_rtc_calibration(struct device *dev,
+                                struct device_attribute *attr,
+                                const char *buf, size_t count)
+{
+        int retval;
+        int calibration = 0;
+
+        if (sscanf(buf, " %i ", &calibration) != 1) {
+                dev_err(dev, "Failed to store RTC calibration attribute\n");
+                return -EINVAL;
+        }
+
+        retval = ab8500_rtc_set_calibration(dev, calibration);
+
+        return retval ? retval : count;
+}
+
+static ssize_t ab8500_sysfs_show_rtc_calibration(struct device *dev,
+                                struct device_attribute *attr, char *buf)
+{
+        int  retval = 0;
+        int  calibration = 0;
+
+        retval = ab8500_rtc_get_calibration(dev, &calibration);
+        if (retval < 0) {
+                dev_err(dev, "Failed to read RTC calibration attribute\n");
+                sprintf(buf, "0\n");
+                return retval;
+        }
+
+        return sprintf(buf, "%d\n", calibration);
+}
+
+static DEVICE_ATTR(rtc_calibration, S_IRUGO | S_IWUSR,
+                   ab8500_sysfs_show_rtc_calibration,
+                   ab8500_sysfs_store_rtc_calibration);
+
+static int ab8500_sysfs_rtc_register(struct device *dev)
+{
+        return device_create_file(dev, &dev_attr_rtc_calibration);
+}
+
+static void ab8500_sysfs_rtc_unregister(struct device *dev)
+{
+        device_remove_file(dev, &dev_attr_rtc_calibration);
+}
+
 static irqreturn_t rtc_alarm_handler(int irq, void *data)
 {
         struct rtc_device *rtc = data;
@@ -327,6 +430,13 @@ static int __devinit ab8500_rtc_probe(struct platform_device *pdev)
 
         platform_set_drvdata(pdev, rtc);
 
+
+        err = ab8500_sysfs_rtc_register(&pdev->dev);
+        if (err) {
+                dev_err(&pdev->dev, "sysfs RTC failed to register\n");
+                return err;
+        }
+
         return 0;
 }
 
@@ -335,6 +445,8 @@ static int __devexit ab8500_rtc_remove(struct platform_device *pdev)
         struct rtc_device *rtc = platform_get_drvdata(pdev);
         int irq = platform_get_irq_byname(pdev, "ALARM");
 
+        ab8500_sysfs_rtc_unregister(&pdev->dev);
+
         free_irq(irq, rtc);
         rtc_device_unregister(rtc);
         platform_set_drvdata(pdev, NULL);