Add ioctl to retrieve USBTMC-USB488 capabilities

This is a convenience function to obtain an instrument's
capabilities from its file descriptor without having to access sysfs
from the user program.

Signed-off-by: Dave Penkler <dpenkler@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/usb/class/usbtmc.c b/drivers/usb/class/usbtmc.c
index 8678429..6edb21c 100644
--- a/drivers/usb/class/usbtmc.c
+++ b/drivers/usb/class/usbtmc.c
@@ -102,6 +102,9 @@
 	u16            iin_wMaxPacketSize;
 	atomic_t       srq_asserted;
 
+	/* coalesced usb488_caps from usbtmc_dev_capabilities */
+	__u8 usb488_caps;
+
 	u8 rigol_quirk;
 
 	/* attributes from the USB TMC spec for this device */
@@ -993,6 +996,7 @@
 	data->capabilities.device_capabilities = buffer[5];
 	data->capabilities.usb488_interface_capabilities = buffer[14];
 	data->capabilities.usb488_device_capabilities = buffer[15];
+	data->usb488_caps = (buffer[14] & 0x07) | ((buffer[15] & 0x0f) << 4);
 	rv = 0;
 
 err_out:
@@ -1168,6 +1172,14 @@
 		retval = usbtmc_ioctl_abort_bulk_in(data);
 		break;
 
+	case USBTMC488_IOCTL_GET_CAPS:
+		retval = copy_to_user((void __user *)arg,
+				&data->usb488_caps,
+				sizeof(data->usb488_caps));
+		if (retval)
+			retval = -EFAULT;
+		break;
+
 	case USBTMC488_IOCTL_READ_STB:
 		retval = usbtmc488_ioctl_read_stb(data, (void __user *)arg);
 		break;