Hello Oleksandr-

I have a few comments below.

On Fri, Jan 12, 2018 at 07:08:26PM +0200, Oleksandr Shamray wrote:

Initial patch for JTAG driver
JTAG class driver provide infrastructure to support hardware/software
JTAG platform drivers. It provide user layer API interface for flashing
and debugging external devices which equipped with JTAG interface
using standard transactions.

Driver exposes set of IOCTL to user space for:
- XFER:
- SIR (Scan Instruction Register, IEEE 1149.1 Data Register scan);
- SDR (Scan Data Register, IEEE 1149.1 Instruction Register scan);
- RUNTEST (Forces the IEEE 1149.1 bus to a run state for a specified
  number of clocks).
- SIOCFREQ/GIOCFREQ for setting and reading JTAG frequency.

Driver core provides set of internal APIs for allocation and
registration:
- jtag_register;
- jtag_unregister;
- jtag_alloc;
- jtag_free;

Platform driver on registration with jtag-core creates the next
entry in dev folder:
/dev/jtagX

Signed-off-by: Oleksandr Shamray <redacted>
Signed-off-by: Jiri Pirko <redacted>
Acked-by: Philippe Ombredanne <redacted>

[..]

+static long jtag_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+	struct jtag *jtag = file->private_data;
+	struct jtag_run_test_idle idle;
+	struct jtag_xfer xfer;
+	u8 *xfer_data;
+	u32 data_size;
+	u32 value;
+	int err;
+
+	if (!arg)
+		return -EINVAL;
+
+	switch (cmd) {
+	case JTAG_GIOCFREQ:
+		if (!jtag->ops->freq_get)
+			err = -EOPNOTSUPP;
+
+		err = jtag->ops->freq_get(jtag, &value);
+		if (err)
+			break;
+
+		if (put_user(value, (__u32 *)arg))
+			err = -EFAULT;
+		break;
+
+	case JTAG_SIOCFREQ:
+		if (!jtag->ops->freq_set)
+			return -EOPNOTSUPP;
+
+		if (get_user(value, (__u32 *)arg))
+			return -EFAULT;
+		if (value == 0)
+			return -EINVAL;
+
+		err = jtag->ops->freq_set(jtag, value);
+		break;
+
+	case JTAG_IOCRUNTEST:
+		if (!jtag->ops->idle)
+			return -EOPNOTSUPP;
+
+		if (copy_from_user(&idle, (void *)arg,
+				   sizeof(struct jtag_run_test_idle)))
+			return -EFAULT;
+
+		if (idle.endstate > JTAG_STATE_PAUSEDR)
+			return -EINVAL;
+
+		err = jtag->ops->idle(jtag, &idle);
+		break;
+
+	case JTAG_IOCXFER:
+		if (!jtag->ops->xfer)

Are all ops optional?  That seems bizarre.  I would have expected at
least one callback to be required.

[..]

+static int jtag_open(struct inode *inode, struct file *file)
+{
+	struct jtag *jtag = container_of(file->private_data, struct jtag,
+					 miscdev);
+
+	if (mutex_lock_interruptible(&jtag->open_lock))
+		return -ERESTARTSYS;
+
+	if (jtag->opened) {
+		mutex_unlock(&jtag->open_lock);
+		return -EBUSY;
+	}
+
+	nonseekable_open(inode, file);
+	file->private_data = jtag;

These two can be moved out of the lock.

+	jtag->opened = true;
+	mutex_unlock(&jtag->open_lock);
+	return 0;
+}
+
+static int jtag_release(struct inode *inode, struct file *file)
+{
+	struct jtag *jtag = file->private_data;
+
+	mutex_lock(&jtag->open_lock);
+	jtag->opened = false;
+	mutex_unlock(&jtag->open_lock);
+	return 0;
+}
+
+static const struct file_operations jtag_fops = {
+	.owner		= THIS_MODULE,
+	.open		= jtag_open,
+	.release	= jtag_release,
+	.llseek		= noop_llseek,
+	.unlocked_ioctl = jtag_ioctl,
+};
+
+struct jtag *jtag_alloc(size_t priv_size, const struct jtag_ops *ops)
+{
+	struct jtag *jtag;
+
+	jtag = kzalloc(sizeof(*jtag), GFP_KERNEL);

Did you mean to allocate: sizeof(*jtag) + priv_size?

+	if (!jtag)
+		return NULL;
+
+	jtag->ops = ops;
+	return jtag;
+}
+EXPORT_SYMBOL_GPL(jtag_alloc);
+
+void jtag_free(struct jtag *jtag)
+{
+	kfree(jtag);
+}
+EXPORT_SYMBOL_GPL(jtag_free);
+
+int jtag_register(struct jtag *jtag)
+{
+	char *name;
+	int err;
+	int id;
+
+	id = ida_simple_get(&jtag_ida, 0, 0, GFP_KERNEL);
+	if (id < 0)
+		return id;
+
+	jtag->id = id;
+
+	name = kzalloc(MAX_JTAG_NAME_LEN, GFP_KERNEL);
+	if (!name) {
+		err = -ENOMEM;
+		goto err_jtag_alloc;
+	}
+
+	err = snprintf(name, MAX_JTAG_NAME_LEN, "jtag%d", id);
+	if (err < 0)
+		goto err_jtag_name;
+
+	mutex_init(&jtag->open_lock);
+	jtag->miscdev.fops =  &jtag_fops;
+	jtag->miscdev.minor = MISC_DYNAMIC_MINOR;
+	jtag->miscdev.name = name;
+
+	err = misc_register(&jtag->miscdev);
+	if (err)
+		dev_err(jtag->dev, "Unable to register device\n");
+	else
+		return 0;
+	jtag->opened = false;

Well, this code flow is just confusing.

I suggest a redo with:

	err = misc_register(&jtag->miscdev);
	if (err) {
		dev_err(jtag->dev, "Unable to register device\n");
		goto err_jtag_name;
	}

If you need to initialize 'opened', do it prior to misc_register.

Thanks,
   Julia