usb: usbtmc: Add ioctl for termination character

add USBTMC_IOCTL_CONFIG_TERMCHAR to control TermChar handling
for next read(). Controls field 'TermChar' and Bit 1 of field
'bmTransferAttributes' of REQUEST_DEV_DEP_MSG_IN BULK-OUT header.

Allows enabling/disabling of terminating a read on reception of
term_char individually for each read request.

Reviewed-by: Steve Bayless <[e-mail]>
Tested-by: Dave Penkler <[e-mail]>
Signed-off-by: Dave Penkler <[e-mail]>
Signed-off-by: Guido Kiener <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/class/usbtmc.c

···
 	u8             srq_byte;
 	atomic_t       srq_asserted;
 	u8             eom_val;
+	u8             term_char;
+	bool           term_char_enabled;
 };
 
 /* Forward declarations */
···
 	mutex_lock(&data->io_mutex);
 	file_data->data = data;
 
+	/* copy default values from device settings */
 	file_data->timeout = USBTMC_TIMEOUT;
+	file_data->term_char = data->TermChar;
+	file_data->term_char_enabled = data->TermCharEnabled;
 	file_data->eom_val = 1;
 
 	INIT_LIST_HEAD(&file_data->file_elem);
···
 	buffer[5] = transfer_size >> 8;
 	buffer[6] = transfer_size >> 16;
 	buffer[7] = transfer_size >> 24;
-	buffer[8] = data->TermCharEnabled * 2;
+	buffer[8] = file_data->term_char_enabled * 2;
 	/* Use term character? */
-	buffer[9] = data->TermChar;
+	buffer[9] = file_data->term_char;
 	buffer[10] = 0; /* Reserved */
 	buffer[11] = 0; /* Reserved */
 
···
 	return 0;
 }
 
+/*
+ * Configure termination character for read()
+ */
+static int usbtmc_ioctl_config_termc(struct usbtmc_file_data *file_data,
+				void __user *arg)
+{
+	struct usbtmc_termchar termc;
+
+	if (copy_from_user(&termc, arg, sizeof(termc)))
+		return -EFAULT;
+
+	if ((termc.term_char_enabled > 1) ||
+		(termc.term_char_enabled &&
+		!(file_data->data->capabilities.device_capabilities & 1)))
+		return -EINVAL;
+
+	file_data->term_char = termc.term_char;
+	file_data->term_char_enabled = termc.term_char_enabled;
+
+	return 0;
+}
+
 static long usbtmc_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 {
 	struct usbtmc_file_data *file_data;
···
 	case USBTMC_IOCTL_EOM_ENABLE:
 		retval = usbtmc_ioctl_eom_enable(file_data,
 						 (void __user *)arg);
+		break;
+
+	case USBTMC_IOCTL_CONFIG_TERMCHAR:
+		retval = usbtmc_ioctl_config_termc(file_data,
+						   (void __user *)arg);
 		break;
 
 	case USBTMC488_IOCTL_GET_CAPS:

include/uapi/linux/usb/tmc.h

···
 #define USBTMC488_REQUEST_GOTO_LOCAL			161
 #define USBTMC488_REQUEST_LOCAL_LOCKOUT			162
 
+struct usbtmc_termchar {
+	__u8 term_char;
+	__u8 term_char_enabled;
+} __attribute__ ((packed));
+
 /* Request values for USBTMC driver's ioctl entry point */
 #define USBTMC_IOC_NR			91
 #define USBTMC_IOCTL_INDICATOR_PULSE	_IO(USBTMC_IOC_NR, 1)
···
 #define USBTMC_IOCTL_GET_TIMEOUT	_IOR(USBTMC_IOC_NR, 9, __u32)
 #define USBTMC_IOCTL_SET_TIMEOUT	_IOW(USBTMC_IOC_NR, 10, __u32)
 #define USBTMC_IOCTL_EOM_ENABLE	        _IOW(USBTMC_IOC_NR, 11, __u8)
+#define USBTMC_IOCTL_CONFIG_TERMCHAR	_IOW(USBTMC_IOC_NR, 12, struct usbtmc_termchar)
 
 #define USBTMC488_IOCTL_GET_CAPS	_IOR(USBTMC_IOC_NR, 17, unsigned char)
 #define USBTMC488_IOCTL_READ_STB	_IOR(USBTMC_IOC_NR, 18, unsigned char)