ieee1394: cycle timer read extension for raw1394

This implements the simultaneous read of the isochronous cycle timer and
the system clock (in usecs). This allows to express the exact receive
time of an ISO packet as a system time with microsecond accuracy.
http://bugzilla.kernel.org/show_bug.cgi?id=7773

The counterpart patch for libraw1394 can be found at
http://thread.gmane.org/gmane.linux.kernel.firewire.devel/8934

Patch update (Stefan R.): Disable preemption and local interrupts.
Prevent integer overflow. Add paranoid error checks and kerneldoc to
hpsb_read_cycle_timer. Move it to other ieee1394_core high-level API
functions. Change comments. Adjust whitespace. Rename struct
_raw1394_cycle_timer.

Signed-off-by: Stefan Richter <[e-mail]>
Acked-by: Pieter Palmers <[e-mail]>
Acked-by: Dan Dennedy <[e-mail]>

drivers/ieee1394/ieee1394-ioctl.h

···
 	_IO  ('#', 0x28)
 #define RAW1394_IOC_ISO_RECV_FLUSH		\
 	_IO  ('#', 0x29)
+#define RAW1394_IOC_GET_CYCLE_TIMER		\
+	_IOR ('#', 0x30, struct raw1394_cycle_timer)
 
 #endif /* __IEEE1394_IOCTL_H */

drivers/ieee1394/ieee1394_core.c

···
 #include <linux/skbuff.h>
 #include <linux/suspend.h>
 #include <linux/kthread.h>
+#include <linux/preempt.h>
+#include <linux/time.h>
 
+#include <asm/system.h>
 #include <asm/byteorder.h>
 
 #include "ieee1394_types.h"
···
 	}
 }
 
+/**
+ * hpsb_read_cycle_timer - read cycle timer register and system time
+ * @host: host whose isochronous cycle timer register is read
+ * @cycle_timer: address of bitfield to return the register contents
+ * @local_time: address to return the system time
+ *
+ * The format of * @cycle_timer, is described in OHCI 1.1 clause 5.13. This
+ * format is also read from non-OHCI controllers. * @local_time contains the
+ * system time in microseconds since the Epoch, read at the moment when the
+ * cycle timer was read.
+ *
+ * Return value: 0 for success or error number otherwise.
+ */
+int hpsb_read_cycle_timer(struct hpsb_host *host, u32 *cycle_timer,
+			  u64 *local_time)
+{
+	int ctr;
+	struct timeval tv;
+	unsigned long flags;
+
+	if (!host || !cycle_timer || !local_time)
+		return -EINVAL;
+
+	preempt_disable();
+	local_irq_save(flags);
+
+	ctr = host->driver->devctl(host, GET_CYCLE_COUNTER, 0);
+	if (ctr)
+		do_gettimeofday(&tv);
+
+	local_irq_restore(flags);
+	preempt_enable();
+
+	if (!ctr)
+		return -EIO;
+	*cycle_timer = ctr;
+	*local_time = tv.tv_sec * 1000000ULL + tv.tv_usec;
+	return 0;
+}
 
 int hpsb_bus_reset(struct hpsb_host *host)
 {
···
 EXPORT_SYMBOL(hpsb_free_packet);
 EXPORT_SYMBOL(hpsb_send_packet);
 EXPORT_SYMBOL(hpsb_reset_bus);
+EXPORT_SYMBOL(hpsb_read_cycle_timer);
 EXPORT_SYMBOL(hpsb_bus_reset);
 EXPORT_SYMBOL(hpsb_selfid_received);
 EXPORT_SYMBOL(hpsb_selfid_complete);

drivers/ieee1394/ieee1394_core.h

···
  * progress, 0 otherwise. */
 int hpsb_reset_bus(struct hpsb_host *host, int type);
 
+int hpsb_read_cycle_timer(struct hpsb_host *host, u32 *cycle_timer,
+			  u64 *local_time);
+
 /*
  * The following functions are exported for host driver module usage.  All of
  * them are safe to use in interrupt contexts, although some are quite

drivers/ieee1394/raw1394.c

···
 	fi->iso_state = RAW1394_ISO_INACTIVE;
 }
 
+static int raw1394_read_cycle_timer(struct file_info *fi, void __user * uaddr)
+{
+	struct raw1394_cycle_timer ct;
+	int err;
+
+	err = hpsb_read_cycle_timer(fi->host, &ct.cycle_timer, &ct.local_time);
+	if (!err)
+		if (copy_to_user(uaddr, &ct, sizeof(ct)))
+			err = -EFAULT;
+	return err;
+}
+
 /* mmap the rawiso xmit/recv buffer */
 static int raw1394_mmap(struct file *file, struct vm_area_struct *vma)
 {
···
 			return 0;
 		}
 		break;
+	default:
+		break;
+	}
+
+	/* state-independent commands */
+	switch(cmd) {
+	case RAW1394_IOC_GET_CYCLE_TIMER:
+		return raw1394_read_cycle_timer(fi, argp);
 	default:
 		break;
 	}

drivers/ieee1394/raw1394.h

···
 	__s16 xmit_cycle;
 };
 
+/* argument to RAW1394_IOC_GET_CYCLE_TIMER ioctl */
+struct raw1394_cycle_timer {
+	/* contents of Isochronous Cycle Timer register,
+	   as in OHCI 1.1 clause 5.13 (also with non-OHCI hosts) */
+	__u32 cycle_timer;
+
+	/* local time in microseconds since Epoch,
+	   simultaneously read with cycle timer */
+	__u64 local_time;
+};
 #endif /* IEEE1394_RAW1394_H */