usb: usbtmc: Add ioctl USBTMC488_IOCTL_WAIT_SRQ

Wait until an SRQ (service request) is received on the interrupt pipe
or until the given period of time is expired. In contrast to the
poll() function this ioctl does not return when other (a)synchronous
I/O operations fail with EPOLLERR.
Signed-off-by: Guido Kiener <guido.kiener@rohde-schwarz.com>
Reviewed-by: Steve Bayless <steve_bayless@keysight.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/class/usbtmc.c

@@ -130,6 +130,7 @@ struct usbtmc_file_data {
 	u32            timeout;
 	u8             srq_byte;
 	atomic_t       srq_asserted;
+	atomic_t       closing;
 
 	u8             eom_val;
 	u8             term_char;
@@ -193,6 +194,8 @@ static int usbtmc_open(struct inode *inode, struct file *filp)
 	mutex_lock(&data->io_mutex);
 	file_data->data = data;
 
+	atomic_set(&file_data->closing, 0);
+
 	/* copy default values from device settings */
 	file_data->timeout = USBTMC_TIMEOUT;
 	file_data->term_char = data->TermChar;
@@ -223,6 +226,7 @@ static int usbtmc_flush(struct file *file, fl_owner_t id)
 	if (file_data == NULL)
 		return -ENODEV;
 
+	atomic_set(&file_data->closing, 1);
 	data = file_data->data;
 
 	/* wait for io to stop */
@@ -576,6 +580,54 @@ static int usbtmc488_ioctl_read_stb(struct usbtmc_file_data *file_data,
 	return rv;
 }
 
+static int usbtmc488_ioctl_wait_srq(struct usbtmc_file_data *file_data,
+				    __u32 __user *arg)
+{
+	struct usbtmc_device_data *data = file_data->data;
+	struct device *dev = &data->intf->dev;
+	int rv;
+	u32 timeout;
+	unsigned long expire;
+
+	if (!data->iin_ep_present) {
+		dev_dbg(dev, "no interrupt endpoint present\n");
+		return -EFAULT;
+	}
+
+	if (get_user(timeout, arg))
+		return -EFAULT;
+
+	expire = msecs_to_jiffies(timeout);
+
+	mutex_unlock(&data->io_mutex);
+
+	rv = wait_event_interruptible_timeout(
+			data->waitq,
+			atomic_read(&file_data->srq_asserted) != 0 ||
+			atomic_read(&file_data->closing),
+			expire);
+
+	mutex_lock(&data->io_mutex);
+
+	/* Note! disconnect or close could be called in the meantime */
+	if (atomic_read(&file_data->closing) || data->zombie)
+		rv = -ENODEV;
+
+	if (rv < 0) {
+		/* dev can be invalid now! */
+		pr_debug("%s - wait interrupted %d\n", __func__, rv);
+		return rv;
+	}
+
+	if (rv == 0) {
+		dev_dbg(dev, "%s - wait timed out\n", __func__);
+		return -ETIMEDOUT;
+	}
+
+	dev_dbg(dev, "%s - srq asserted\n", __func__);
+	return 0;
+}
+
 static int usbtmc488_ioctl_simple(struct usbtmc_device_data *data,
 				void __user *arg, unsigned int cmd)
 {
@@ -2142,6 +2194,11 @@ static long usbtmc_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		retval = usbtmc488_ioctl_trigger(file_data);
 		break;
 
+	case USBTMC488_IOCTL_WAIT_SRQ:
+		retval = usbtmc488_ioctl_wait_srq(file_data,
+						  (__u32 __user *)arg);
+		break;
+
 	case USBTMC_IOCTL_CANCEL_IO:
 		retval = usbtmc_ioctl_cancel_io(file_data);
 		break;

include/uapi/linux/usb/tmc.h

@@ -96,6 +96,7 @@ struct usbtmc_message {
 #define USBTMC488_IOCTL_GOTO_LOCAL	_IO(USBTMC_IOC_NR, 20)
 #define USBTMC488_IOCTL_LOCAL_LOCKOUT	_IO(USBTMC_IOC_NR, 21)
 #define USBTMC488_IOCTL_TRIGGER		_IO(USBTMC_IOC_NR, 22)
+#define USBTMC488_IOCTL_WAIT_SRQ	_IOW(USBTMC_IOC_NR, 23, __u32)
 
 /* Cancel and cleanup asynchronous calls */
 #define USBTMC_IOCTL_CANCEL_IO		_IO(USBTMC_IOC_NR, 35)