RE: [patch v9 1/4] drivers: jtag: Add JTAG core driver

[Oleksandr Shamray <oleksandrs@xxxxxxxxxxxx>]

Hi Greg.

> -----Original Message-----
> From: Greg KH [mailto:gregkh@xxxxxxxxxxxxxxxxxxx]
> Sent: Friday, October 20, 2017 2:55 PM
> To: Oleksandr Shamray <oleksandrs@xxxxxxxxxxxx>
> Cc: arnd@xxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-arm-
> kernel@xxxxxxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx;
> openbmc@xxxxxxxxxxxxxxxx; joel@xxxxxxxxx; jiri@xxxxxxxxxxx;
> tklauser@xxxxxxxxxx; linux-serial@xxxxxxxxxxxxxxx; mec@xxxxxxxxx; Vadim
> Pasternak <vadimp@xxxxxxxxxxxx>; system-sw-low-level <system-sw-low-
> level@xxxxxxxxxxxx>; robh+dt@xxxxxxxxxx; openocd-devel-
> owner@xxxxxxxxxxxxxxxxxxxxx; linux-api@xxxxxxxxxxxxxxx;
> davem@xxxxxxxxxxxxx; mchehab@xxxxxxxxxx; Jiri Pirko <jiri@xxxxxxxxxxxx>
> Subject: Re: [patch v9 1/4] drivers: jtag: Add JTAG core driver
> 
> On Thu, Sep 21, 2017 at 12:25:29PM +0300, Oleksandr Shamray wrote:
> > +struct jtag {
> > +	struct device *dev;
> > +	struct cdev cdev;
> 
> Why are you using a cdev here and not just a normal misc device? 

What the benefits to use misc instead of cdev?

> I forgot if this is what you were doing before, sorry...
> 
> > +	int id;
> > +	atomic_t open;
> 
> Why do you need this?

This counter used to avoid open at the same time by 2 or more users.
> 
> > +	const struct jtag_ops *ops;
> > +	unsigned long priv[0] __aligned(ARCH_DMA_MINALIGN);
> 
> Huh?  Why is this needed to be dma aligned?  Why not just use the private
> pointer in struct device?
> 

It is critical?

> > +};
> > +
> > +static dev_t jtag_devt;
> > +static DEFINE_IDA(jtag_ida);
> > +
> > +void *jtag_priv(struct jtag *jtag)
> > +{
> > +	return jtag->priv;
> > +}
> > +EXPORT_SYMBOL_GPL(jtag_priv);
> > +
> > +static u8 *jtag_copy_from_user(__u64 udata, unsigned long bit_size) {
> > +	unsigned long size;
> > +	void *kdata;
> > +
> > +	size = DIV_ROUND_UP(bit_size, BITS_PER_BYTE);
> > +	kdata = memdup_user(u64_to_user_ptr(udata), size);
> 
> You only use this once, why not just open-code it?

I think it makes code more understandable.

> 
> > +
> > +	return kdata;
> > +}
> > +
> > +static unsigned long jtag_copy_to_user(__u64 udata, u8 *kdata,
> > +				       unsigned long bit_size)
> > +{
> > +	unsigned long size;
> > +
> > +	size = DIV_ROUND_UP(bit_size, BITS_PER_BYTE);
> > +
> > +	return copy_to_user(u64_to_user_ptr(udata), (void *)(kdata), size);
> 
> Same here, making this a separate function seems odd.

Same, I think it makes code more understandable.

> 
> > +}
> > +
> > +static struct class jtag_class = {
> > +	.name = "jtag",
> > +	.owner = THIS_MODULE,
> > +};
> > +
> > +static int jtag_run_test_idle_op(struct jtag *jtag,
> > +				 struct jtag_run_test_idle *idle) {
> > +	if (jtag->ops->idle)
> > +		return jtag->ops->idle(jtag, idle);
> > +	else
> > +		return -EOPNOTSUPP;
> 
> Why is this a function?  Why not just do this work in the ioctl?

Agree. I will move it just to ioctl function body.

> 
> > +}
> > +
> > +static int jtag_xfer_op(struct jtag *jtag, struct jtag_xfer *xfer, u8
> > +*data) {
> > +	if (jtag->ops->xfer)
> > +		return jtag->ops->xfer(jtag, xfer, data);
> > +	else
> > +		return -EOPNOTSUPP;
> 
> Same here, doesn't need to be a function.

Agree.

> 
> > +}
> > +
> > +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 value;
> > +	int err;
> > +
> > +	switch (cmd) {
> > +	case JTAG_GIOCFREQ:
> > +		if (jtag->ops->freq_get)
> > +			err = jtag->ops->freq_get(jtag, &value);
> > +		else
> > +			err = -EOPNOTSUPP;
> > +		if (err)
> > +			break;
> > +
> > +		err = put_user(value, (__u32 *)arg);
> > +		break;
> 
> Are you sure the return value of put_user is correct here?  Shouldn't you return
> -EFAULT if err is not 0?

Yes, thanks for point of this.

> 
> > +
> > +	case JTAG_SIOCFREQ:
> > +		err = get_user(value, (__u32 *)arg);
> > +
> 
> why a blank line?

Will remove

> 
> > +		if (value == 0)
> > +			err = -EINVAL;
> 
> Check err first.

Ok.

> 
> > +		if (err)
> > +			break;
> 
> And set it properly, again err should be -EFAULT, right?

Right 😊0

> 
> > +
> > +		if (jtag->ops->freq_set)
> > +			err = jtag->ops->freq_set(jtag, value);
> > +		else
> > +			err = -EOPNOTSUPP;
> > +		break;
> > +
> > +	case JTAG_IOCRUNTEST:
> > +		if (copy_from_user(&idle, (void *)arg,
> > +				   sizeof(struct jtag_run_test_idle)))
> > +			return -ENOMEM;
> > +		err = jtag_run_test_idle_op(jtag, &idle);
> 
> Who validates the structure fields?  Is that up to the individual jtag driver?  Why
> not do it in the core correctly so that it only has to be done in one place and you
> do not have to audit every individual driver?

Input parameters validated by jtag  platform driver. I think it not critical.

> 
> > +		break;
> > +
> > +	case JTAG_IOCXFER:
> > +		if (copy_from_user(&xfer, (void *)arg,
> > +				   sizeof(struct jtag_xfer)))
> > +			return -EFAULT;
> > +
> > +		if (xfer.length >= JTAG_MAX_XFER_DATA_LEN)
> > +			return -EFAULT;
> > +
> > +		xfer_data = jtag_copy_from_user(xfer.tdio, xfer.length);
> > +		if (!xfer_data)
> > +			return -ENOMEM;
> 
> Are you sure that's the correct error value?

I think yes, but what you suggest?

> 
> > +
> > +		err = jtag_xfer_op(jtag, &xfer, xfer_data);
> > +		if (jtag_copy_to_user(xfer.tdio, xfer_data, xfer.length)) {
> > +			kfree(xfer_data);
> > +			return -EFAULT;
> > +		}
> > +
> > +		kfree(xfer_data);
> > +		if (copy_to_user((void *)arg, &xfer, sizeof(struct jtag_xfer)))
> > +			return -EFAULT;
> > +		break;
> > +
> > +	case JTAG_GIOCSTATUS:
> > +		if (jtag->ops->status_get)
> > +			err = jtag->ops->status_get(jtag, &value);
> > +		else
> > +			err = -EOPNOTSUPP;
> > +		if (err)
> > +			break;
> > +
> > +		err = put_user(value, (__u32 *)arg);
> 
> Same put_user err issue here.

Yes.

> 
> > +		break;
> > +
> > +	default:
> > +		return -EINVAL;
> > +	}
> > +	return err;
> > +}
> > +
> > +#ifdef CONFIG_COMPAT
> > +static long jtag_ioctl_compat(struct file *file, unsigned int cmd,
> > +			      unsigned long arg)
> > +{
> > +	return jtag_ioctl(file, cmd, (unsigned long)compat_ptr(arg)); }
> > +#endif
> 
> Why do you need a compat callback for a new ioctl?  Create your structures
> properly and this should not be needed, right?


I does this because Arnd (arndbergmann@xxxxxxxxx) writed in review (On Wed, Aug 2, 2017 at 3:18 PM)

[..]
> +       .unlocked_ioctl = jtag_ioctl,
> +       .open           = jtag_open,
> +       .release        = jtag_release,
> +};

add a compat_ioctl pointer here, after ensuring that all ioctl commands are compatible between 32-bit and 64-bit user space.
[..]


> 
> > +
> > +static int jtag_open(struct inode *inode, struct file *file) {
> > +	struct jtag *jtag = container_of(inode->i_cdev, struct jtag, cdev);
> > +
> > +	if (atomic_read(&jtag->open)) {
> > +		dev_info(NULL, "jtag already opened\n");
> > +		return -EBUSY;
> 
> Why do you care if multiple opens can happen?

Jtag HW not support to using with multiple requests from different users. So we prohibit this.

> 
> > +	}
> > +
> > +	atomic_inc(&jtag->open);
> 
> Oh look, you just raced with two different people opening at the same time :(
> 
> An atomic value is never a replacement for a lock, sorry.
> 
> > +	file->private_data = jtag;
> > +	return 0;
> > +}
> > +
> > +static int jtag_release(struct inode *inode, struct file *file) {
> > +	struct jtag *jtag = file->private_data;
> > +
> > +	atomic_dec(&jtag->open);
> 
> Again, not needed.
> 
> > +	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,
> > +#ifdef CONFIG_COMPAT
> > +	.compat_ioctl	= jtag_ioctl_compat,
> > +#endif
> > +};
> > +
> > +struct jtag *jtag_alloc(size_t priv_size, const struct jtag_ops *ops)
> > +{
> > +	struct jtag *jtag;
> > +
> > +	jtag = kzalloc(sizeof(*jtag) + round_up(priv_size,
> ARCH_DMA_MINALIGN),
> > +		       GFP_KERNEL);
> > +	if (!jtag)
> > +		return NULL;
> > +
> > +	jtag->ops = ops;
> > +	return jtag;
> > +}
> > +EXPORT_SYMBOL_GPL(jtag_alloc);
> 
> register should allocate and register the device, why pass a structure back that
> the caller then has to do something else with to use it?
> 

Before registration we need to initialize JTAG device HW registers and fill private data with HW specific parameters.
And is I see in other Linux drivers it is a common way to separate allocation device and register it

> > +
> > +void jtag_free(struct jtag *jtag)
> > +{
> > +	kfree(jtag);
> > +}
> > +EXPORT_SYMBOL_GPL(jtag_free);
> > +
> > +int jtag_register(struct jtag *jtag)
> > +{
> > +	int id;
> > +	int err;
> > +
> > +	id = ida_simple_get(&jtag_ida, 0, 0, GFP_KERNEL);
> > +	if (id < 0)
> > +		return id;
> > +
> > +	jtag->id = id;
> > +	cdev_init(&jtag->cdev, &jtag_fops);
> > +	jtag->cdev.owner = THIS_MODULE;
> > +	err = cdev_add(&jtag->cdev, MKDEV(MAJOR(jtag_devt), jtag->id), 1);
> > +	if (err)
> > +		goto err_cdev;
> 
> misc device would be so much simpler and easier here :(
> 
> 
> > +
> > +	/* Register this jtag device with the driver core */
> > +	jtag->dev = device_create(&jtag_class, NULL,
> MKDEV(MAJOR(jtag_devt),
> > +							   jtag->id),
> > +				  NULL, "jtag%d", jtag->id);
> > +	if (!jtag->dev)
> > +		goto err_device_create;
> > +
> > +	atomic_set(&jtag->open, 0);
> > +	dev_set_drvdata(jtag->dev, jtag);
> > +	return err;
> > +
> > +err_device_create:
> > +	cdev_del(&jtag->cdev);
> > +err_cdev:
> > +	ida_simple_remove(&jtag_ida, id);
> > +	return err;
> > +}
> > +EXPORT_SYMBOL_GPL(jtag_register);
> > +
> > +void jtag_unregister(struct jtag *jtag) {
> > +	struct device *dev = jtag->dev;
> > +
> > +	cdev_del(&jtag->cdev);
> > +	device_unregister(dev);
> > +	ida_simple_remove(&jtag_ida, jtag->id); }
> > +EXPORT_SYMBOL_GPL(jtag_unregister);
> > +
> > +static int __init jtag_init(void)
> > +{
> > +	int err;
> > +
> > +	err = alloc_chrdev_region(&jtag_devt, JTAG_FIRST_MINOR,
> > +				  JTAG_MAX_DEVICES, "jtag");
> > +	if (err)
> > +		return err;
> > +
> > +	err = class_register(&jtag_class);
> > +	if (err)
> > +		unregister_chrdev_region(jtag_devt, JTAG_MAX_DEVICES);
> > +
> > +	return err;
> > +}
> > +
> > +static void __exit jtag_exit(void)
> > +{
> > +	class_unregister(&jtag_class);
> > +	unregister_chrdev_region(jtag_devt, JTAG_MAX_DEVICES);
> 
> Your idr leaked memory :(
> 

Yes I will add ida_destroy() here.
> 
> 
> > +}
> > +
> > +module_init(jtag_init);
> > +module_exit(jtag_exit);
> > +
> > +MODULE_AUTHOR("Oleksandr Shamray <oleksandrs@xxxxxxxxxxxx>");
> > +MODULE_DESCRIPTION("Generic jtag support"); MODULE_LICENSE("GPL
> v2");
> > diff --git a/include/linux/jtag.h b/include/linux/jtag.h new file mode
> > 100644 index 0000000..c016fed
> > --- /dev/null
> > +++ b/include/linux/jtag.h
> > @@ -0,0 +1,48 @@
> > +/*
> > + * drivers/jtag/jtag.c
> > + *
> > + * Copyright (c) 2017 Mellanox Technologies. All rights reserved.
> > + * Copyright (c) 2017 Oleksandr Shamray <oleksandrs@xxxxxxxxxxxx>
> > + *
> > + * Released under the GPLv2 only.
> > + * SPDX-License-Identifier: GPL-2.0
> > + */
> > +
> > +#ifndef __JTAG_H
> > +#define __JTAG_H
> > +
> > +#include <uapi/linux/jtag.h>
> > +
> > +#ifndef ARCH_DMA_MINALIGN
> > +#define ARCH_DMA_MINALIGN 1
> > +#endif
> > +
> > +#define jtag_u64_to_ptr(arg) ((void *)(uintptr_t)arg)
> > +
> > +#define JTAG_MAX_XFER_DATA_LEN 65535
> > +
> > +struct jtag;
> > +/**
> > + * struct jtag_ops - callbacks for jtag control functions:
> > + *
> > + * @freq_get: get frequency function. Filled by device driver
> > + * @freq_set: set frequency function. Filled by device driver
> > + * @status_get: set status function. Filled by device driver
> > + * @idle: set JTAG to idle state function. Filled by device driver
> > + * @xfer: send JTAG xfer function. Filled by device driver  */ struct
> > +jtag_ops {
> > +	int (*freq_get)(struct jtag *jtag, u32 *freq);
> > +	int (*freq_set)(struct jtag *jtag, u32 freq);
> > +	int (*status_get)(struct jtag *jtag, u32 *state);
> > +	int (*idle)(struct jtag *jtag, struct jtag_run_test_idle *idle);
> > +	int (*xfer)(struct jtag *jtag, struct jtag_xfer *xfer); };
> > +
> > +void *jtag_priv(struct jtag *jtag);
> > +int jtag_register(struct jtag *jtag); void jtag_unregister(struct
> > +jtag *jtag); struct jtag *jtag_alloc(size_t priv_size, const struct
> > +jtag_ops *ops); void jtag_free(struct jtag *jtag);
> > +
> > +#endif /* __JTAG_H */
> > diff --git a/include/uapi/linux/jtag.h b/include/uapi/linux/jtag.h new
> > file mode 100644 index 0000000..180bf22
> > --- /dev/null
> > +++ b/include/uapi/linux/jtag.h
> > @@ -0,0 +1,115 @@
> > +/*
> > + * JTAG class driver
> > + *
> > + * Copyright (c) 2017 Mellanox Technologies. All rights reserved.
> > + * Copyright (c) 2017 Oleksandr Shamray <oleksandrs@xxxxxxxxxxxx>
> > + *
> > + * Released under the GPLv2/BSD.
> > + * SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause  */
> > +
> > +#ifndef __UAPI_LINUX_JTAG_H
> > +#define __UAPI_LINUX_JTAG_H
> > +
> > +/**
> > + * enum jtag_xfer_mode:
> > + *
> > + * @JTAG_XFER_HW_MODE: hardware mode transfer
> > + * @JTAG_XFER_SW_MODE: software mode transfer  */ enum
> jtag_xfer_mode
> > +{
> > +	JTAG_XFER_HW_MODE,
> > +	JTAG_XFER_SW_MODE,
> > +};
> > +
> > +/**
> > + * enum jtag_endstate:
> > + *
> > + * @JTAG_STATE_IDLE: JTAG state machine IDLE state
> > + * @JTAG_STATE_PAUSEIR: JTAG state machine PAUSE_IR state
> > + * @JTAG_STATE_PAUSEDR: JTAG state machine PAUSE_DR state  */ enum
> > +jtag_endstate {
> > +	JTAG_STATE_IDLE,
> > +	JTAG_STATE_PAUSEIR,
> > +	JTAG_STATE_PAUSEDR,
> > +};
> > +
> > +/**
> > + * enum jtag_xfer_type:
> > + *
> > + * @JTAG_SIR_XFER: SIR transfer
> > + * @JTAG_SDR_XFER: SDR transfer
> > + */
> > +enum jtag_xfer_type {
> > +	JTAG_SIR_XFER,
> > +	JTAG_SDR_XFER,
> > +};
> > +
> > +/**
> > + * enum jtag_xfer_direction:
> > + *
> > + * @JTAG_READ_XFER: read transfer
> > + * @JTAG_WRITE_XFER: write transfer
> > + */
> > +enum jtag_xfer_direction {
> > +	JTAG_READ_XFER,
> > +	JTAG_WRITE_XFER,
> > +};
> > +
> > +/**
> > + * struct jtag_run_test_idle - forces JTAG state machine to
> > + * RUN_TEST/IDLE state
> > + *
> > + * @mode: access mode
> > + * @reset: 0 - run IDLE/PAUSE from current state
> > + *         1 - go through TEST_LOGIC/RESET state before  IDLE/PAUSE
> > + * @end: completion flag
> > + * @tck: clock counter
> > + *
> > + * Structure represents interface to JTAG device for jtag idle
> > + * execution.
> > + */
> > +struct jtag_run_test_idle {
> > +	__u8	mode;
> > +	__u8	reset;
> > +	__u8	endstate;
> > +	__u8	tck;
> > +};
> > +
> > +/**
> > + * struct jtag_xfer - jtag xfer:
> > + *
> > + * @mode: access mode
> > + * @type: transfer type
> > + * @direction: xfer direction
> > + * @length: xfer bits len
> > + * @tdio : xfer data array
> > + * @endir: xfer end state
> > + *
> > + * Structure represents interface to Aspeed JTAG device for jtag sdr
> > +xfer
> > + * execution.
> > + */
> > +struct jtag_xfer {
> > +	__u8	mode;
> > +	__u8	type;
> > +	__u8	direction;
> > +	__u8	endstate;
> > +	__u32	length;
> > +	__u64	tdio;
> 
> I don't see anything odd here that requires a compat ioctl callback, do you?
> 
> thanks,
> 
> greg k-h

Thanks for your review.

Oleksandr S.
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