linux-kernel - RE: [patch v16 1/4] drivers: jtag: Add JTAG core driver

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Date:   Tue, 16 Jan 2018 07:04:09 +0000
From:   Oleksandr Shamray <oleksandrs@...lanox.com>
To:     Julia Cartwright <juliac@....teric.us>
CC:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "arnd@...db.de" <arnd@...db.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "openbmc@...ts.ozlabs.org" <openbmc@...ts.ozlabs.org>,
        "joel@....id.au" <joel@....id.au>,
        "jiri@...nulli.us" <jiri@...nulli.us>,
        "tklauser@...tanz.ch" <tklauser@...tanz.ch>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        Vadim Pasternak <vadimp@...lanox.com>,
        system-sw-low-level <system-sw-low-level@...lanox.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "openocd-devel-owner@...ts.sourceforge.net" 
        <openocd-devel-owner@...ts.sourceforge.net>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        Jiri Pirko <jiri@...lanox.com>
Subject: RE: [patch v16 1/4] drivers: jtag: Add JTAG core driver

Hi Julia

> -----Original Message-----
> From: Julia Cartwright [mailto:juliac@....teric.us]
> Sent: 15 января 2018 г. 22:52
> To: Oleksandr Shamray <oleksandrs@...lanox.com>
> Cc: gregkh@...uxfoundation.org; arnd@...db.de; linux-
> kernel@...r.kernel.org; linux-arm-kernel@...ts.infradead.org;
> devicetree@...r.kernel.org; openbmc@...ts.ozlabs.org; joel@....id.au;
> jiri@...nulli.us; tklauser@...tanz.ch; linux-serial@...r.kernel.org; Vadim
> Pasternak <vadimp@...lanox.com>; system-sw-low-level <system-sw-low-
> level@...lanox.com>; robh+dt@...nel.org; openocd-devel-
> owner@...ts.sourceforge.net; linux-api@...r.kernel.org;
> davem@...emloft.net; mchehab@...nel.org; Jiri Pirko
> <jiri@...lanox.com>
> Subject: Re: [patch v16 1/4] drivers: jtag: Add JTAG core driver
> 
> 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.
> >

[..]
> > +		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.

You right. But I'm preferred to check pointers before use it.

> 
> [..]
> > +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.

Agree.

> 
> > +	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?

Thank, it's a mistake.

> 
> > +	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

> Thanks,
>    Julia

Thanks for Review.

Br,
Oleksandr