rtc/ab8500: add calibration attribute to AB8500 RTC
Mark Godfrey [Tue, 10 Jan 2012 23:10:42 +0000 (15:10 -0800)]
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>

Documentation/ABI/testing/sysfs-class-rtc-rtc0-device-rtc_calibration [new file with mode: 0644]
drivers/rtc/rtc-ab8500.c

diff --git a/Documentation/ABI/testing/sysfs-class-rtc-rtc0-device-rtc_calibration b/Documentation/ABI/testing/sysfs-class-rtc-rtc0-device-rtc_calibration
new file mode 100644 (file)
index 0000000..4cf1e72
--- /dev/null
@@ -0,0 +1,12 @@
+What:           Attribute for calibrating ST-Ericsson AB8500 Real Time Clock
+Date:           Oct 2011
+KernelVersion:  3.0
+Contact:        Mark Godfrey <mark.godfrey@stericsson.com>
+Description:    The rtc_calibration attribute allows the userspace to
+                calibrate the AB8500.s 32KHz Real Time Clock.
+                Every 60 seconds the AB8500 will correct the RTC's value
+                by adding to it the value of this attribute.
+                The range of the attribute is -127 to +127 in units of
+                30.5 micro-seconds (half-parts-per-million of the 32KHz clock)
+Users:          The /vendor/st-ericsson/base_utilities/core/rtc_calibration
+                daemon uses this interface.
index 919b2e5..df7bfc3 100644 (file)
@@ -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);