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-rw-r--r--include/linux/rtc.h17
1 files changed, 17 insertions, 0 deletions
diff --git a/include/linux/rtc.h b/include/linux/rtc.h
index f2d0d1527721..b01fe004cb5e 100644
--- a/include/linux/rtc.h
+++ b/include/linux/rtc.h
@@ -115,6 +115,23 @@ extern void rtc_time_to_tm(unsigned long time, struct rtc_time *tm);
extern struct class *rtc_class;
+/*
+ * For these RTC methods the device parameter is the physical device
+ * on whatever bus holds the hardware (I2C, Platform, SPI, etc), which
+ * was passed to rtc_device_register(). Its driver_data normally holds
+ * device state, including the rtc_device pointer for the RTC.
+ *
+ * Most of these methods are called with rtc_device.ops_lock held,
+ * through the rtc_*(struct rtc_device *, ...) calls.
+ *
+ * The (current) exceptions are mostly filesystem hooks:
+ * - the proc() hook for procfs
+ * - non-ioctl() chardev hooks: open(), release(), read_callback()
+ * - periodic irq calls: irq_set_state(), irq_set_freq()
+ *
+ * REVISIT those periodic irq calls *do* have ops_lock when they're
+ * issued through ioctl() ...
+ */
struct rtc_class_ops {
int (*open)(struct device *);
void (*release)(struct device *);
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