[v11,1/4] drivers: jtag: Add JTAG core driver

Message ID 1509724449-26221-2-git-send-email-oleksandrs@mellanox.com
State New
Headers show
Series
  • JTAG driver introduction
Related show

Commit Message

Oleksandr Shamray Nov. 3, 2017, 3:54 p.m.
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 <oleksandrs@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
---
v10->v11
Notifications from kbuild test robot <lkp@intel.com>
- Add include types.h header to jtag.h
- fix incompatible type of xfer callback
- remove rdundant class defination
- Fix return order in case of xfer error

V9->v10
Comments pointed by Greg KH <gregkh@linuxfoundation.org>
- remove unnecessary alignment for pirv data
- move jtag_copy_to_user and jtag_copy_from_user code just to ioctl
- move int jtag_run_test_idle_op and jtag_xfer_op code
  just to ioctl
- change return error codes to more applicable
- add missing error checks
- fix error check order in ioctl
- remove unnecessary blank lines
- add param validation to ioctl
- remove compat_ioctl
- remove only one open per JTAG port blocking.
  User will care about this.
- Fix idr memory leak on jtag_exit
- change cdev device type to misc

V8->v9
Comments pointed by Arnd Bergmann <arnd@arndb.de>
- use get_user() instead of __get_user().
- change jtag->open type from int to atomic_t
- remove spinlock on jtg_open
- remove mutex on jtag_register
- add unregister_chrdev_region on jtag_init err
- add unregister_chrdev_region on jtag_exit
- remove unnecessary pointer casts
- add *data parameter to xfer function prototype

v7->v8
Comments pointed by Moritz Fischer <moritz.fischer@ettus.com>
- Fix misspelling s/friver/driver

v6->v7
Notifications from kbuild test robot <lkp@intel.com>
- Remove include asm/types.h from jtag.h
- Add include <linux/types.h> to jtag.c

v5->v6
v4->v5

v3->v4
Comments pointed by Arnd Bergmann <arnd@arndb.de>
- change transaction pointer tdio type  to __u64
- change internal status type from enum to __u32
- reorder jtag_xfer members to avoid the implied padding
- add __packed attribute to jtag_xfer and jtag_run_test_idle

v2->v3
Notifications from kbuild test robot <lkp@intel.com>
- Change include path to <linux/types.h> in jtag.h

v1->v2
Comments pointed by Greg KH <gregkh@linuxfoundation.org>
- Change license type from GPLv2/BSD to GPLv2
- Change type of variables which crossed user/kernel to __type
- Remove "default n" from Kconfig

Comments pointed by Andrew Lunn <andrew@lunn.ch>
- Change list_add_tail in jtag_unregister to list_del

Comments pointed by Neil Armstrong <narmstrong@baylibre.com>
- Add SPDX-License-Identifier instead of license text

Comments pointed by Arnd Bergmann <arnd@arndb.de>
- Change __copy_to_user to memdup_user
- Change __put_user to put_user
- Change type of variables to __type for compatible 32 and 64-bit systems
- Add check for maximum xfer data size
- Change lookup data mechanism to get jtag data from inode
- Add .compat_ioctl to file ops
- Add mem alignment for jtag priv data

Comments pointed by Tobias Klauser <tklauser@distanz.ch>
- Change function names to avoid match with variable types
- Fix description for jtag_ru_test_idle in uapi jtag.h
- Fix misprints IDEL/IDLE, trough/through
---
 Documentation/ioctl/ioctl-number.txt |    2 +
 MAINTAINERS                          |   10 ++
 drivers/Kconfig                      |    2 +
 drivers/Makefile                     |    1 +
 drivers/jtag/Kconfig                 |   16 ++
 drivers/jtag/Makefile                |    1 +
 drivers/jtag/jtag.c                  |  267 ++++++++++++++++++++++++++++++++++
 include/linux/jtag.h                 |   48 ++++++
 include/uapi/linux/jtag.h            |  117 +++++++++++++++
 9 files changed, 464 insertions(+), 0 deletions(-)
 create mode 100644 drivers/jtag/Kconfig
 create mode 100644 drivers/jtag/Makefile
 create mode 100644 drivers/jtag/jtag.c
 create mode 100644 include/linux/jtag.h
 create mode 100644 include/uapi/linux/jtag.h

Comments

Greg Kroah-Hartman Nov. 4, 2017, 11:36 a.m. | #1
On Fri, Nov 03, 2017 at 05:54:06PM +0200, Oleksandr Shamray wrote:
> diff --git a/include/uapi/linux/jtag.h b/include/uapi/linux/jtag.h
> new file mode 100644
> index 0000000..0b25a83
> --- /dev/null
> +++ b/include/uapi/linux/jtag.h
> @@ -0,0 +1,117 @@
> +/*
> + * JTAG class driver
> + *
> + * Copyright (c) 2017 Mellanox Technologies. All rights reserved.
> + * Copyright (c) 2017 Oleksandr Shamray <oleksandrs@mellanox.com>
> + *
> + * Released under the GPLv2/BSD.
> + * SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause

Minor nit, this should go on the first line of the .h file now, to match
the rest of the kernel (just happened, not your fault.)

Also, uapi files are not just GPLv2, they have the userspace exception,
so this should just be:
	SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note
no need to add any BSD stuff to it at all.

thanks,

greg k-h
Chip Bilbrey Nov. 5, 2017, 10:32 p.m. | #2
Oleksandr Shamray writes:
> diff --git a/include/uapi/linux/jtag.h b/include/uapi/linux/jtag.h
> new file mode 100644
> index 0000000..0b25a83
> --- /dev/null
> +++ b/include/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,
> +};

Is this essentially selecting between bit-bang mode or not?  Is there a
generally applicable reason to select SW mode over HW (or vice versa)?
This sounds like it's tied to device-specific capability which shouldn't
be exposed in a generic user API.

> +/**
> + * 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.

Probably should remove the reference to Aspeed here.

> +/* ioctl interface */
> +#define __JTAG_IOCTL_MAGIC	0xb2
> +
> +#define JTAG_IOCRUNTEST	_IOW(__JTAG_IOCTL_MAGIC, 0,\
> +			     struct jtag_run_test_idle)
> +#define JTAG_SIOCFREQ	_IOW(__JTAG_IOCTL_MAGIC, 1, unsigned int)
> +#define JTAG_GIOCFREQ	_IOR(__JTAG_IOCTL_MAGIC, 2, unsigned int)
> +#define JTAG_IOCXFER	_IOWR(__JTAG_IOCTL_MAGIC, 3, struct jtag_xfer)
> +#define JTAG_GIOCSTATUS _IOWR(__JTAG_IOCTL_MAGIC, 4, enum jtag_endstate)

I notice the single-open()-per-device lock was dropped by request in an
earlier revision of your patches, but multiple processes trying to drive
a single JTAG master could wreak serious havoc if transactions get
interleaved. Would something like an added JTAG_LOCKCHAIN/UNLOCKCHAIN
ioctl() for exclusive client access be reasonable to prevent this?

-Chip
Oleksandr Shamray Nov. 6, 2017, 2:28 p.m. | #3
Hi, 
Thanks for review>

> -----Original Message-----
> From: Chip Bilbrey [mailto:chip@bilbrey.org]
> Sent: Monday, November 6, 2017 12:33 AM
> To: Oleksandr Shamray <oleksandrs@mellanox.com>
> Cc: gregkh@linuxfoundation.org; arnd@arndb.de; linux-
> kernel@vger.kernel.org; linux-arm-kernel@lists.infradead.org;
> devicetree@vger.kernel.org; openbmc@lists.ozlabs.org; joel@jms.id.au;
> jiri@resnulli.us; tklauser@distanz.ch; linux-serial@vger.kernel.org;
> mec@shout.net; Vadim Pasternak <vadimp@mellanox.com>; system-sw-low-
> level <system-sw-low-level@mellanox.com>; robh+dt@kernel.org; openocd-
> devel-owner@lists.sourceforge.net; linux-api@vger.kernel.org;
> davem@davemloft.net; mchehab@kernel.org; Jiri Pirko <jiri@mellanox.com>
> Subject: Re: [v11,1/4] drivers: jtag: Add JTAG core driver
> 
> 
> Oleksandr Shamray writes:
> > diff --git a/include/uapi/linux/jtag.h b/include/uapi/linux/jtag.h new
> > file mode 100644 index 0000000..0b25a83
> > --- /dev/null
> > +++ b/include/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,
> > +};
> 
> Is this essentially selecting between bit-bang mode or not?  Is there a generally
> applicable reason to select SW mode over HW (or vice versa)?
> This sounds like it's tied to device-specific capability which shouldn't be exposed
> in a generic user API.

It is a mode of working some JTAG master devices. F.e Aspeed JTAG core can work in fully automatic mode when all StateMachine 
transitions and pin control done by hardware and in the more simpler mode when JTAG pin control does by the user (like bit-bang). 

It HW defined feature and can be applied not in all cases. 

Seems it can be deleted from xfer option and controlled by separate like IOCTL_SET_PARAM command.
> 
> > +/**
> > + * 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.
> 
> Probably should remove the reference to Aspeed here.

Thanks, will remove it.

> 
> > +/* ioctl interface */
> > +#define __JTAG_IOCTL_MAGIC	0xb2
> > +
> > +#define JTAG_IOCRUNTEST	_IOW(__JTAG_IOCTL_MAGIC, 0,\
> > +			     struct jtag_run_test_idle)
> > +#define JTAG_SIOCFREQ	_IOW(__JTAG_IOCTL_MAGIC, 1, unsigned int)
> > +#define JTAG_GIOCFREQ	_IOR(__JTAG_IOCTL_MAGIC, 2, unsigned int)
> > +#define JTAG_IOCXFER	_IOWR(__JTAG_IOCTL_MAGIC, 3, struct
> jtag_xfer)
> > +#define JTAG_GIOCSTATUS _IOWR(__JTAG_IOCTL_MAGIC, 4, enum
> > +jtag_endstate)
> 
> I notice the single-open()-per-device lock was dropped by request in an earlier
> revision of your patches, but multiple processes trying to drive a single JTAG
> master could wreak serious havoc if transactions get interleaved. Would
> something like an added JTAG_LOCKCHAIN/UNLOCKCHAIN
> ioctl() for exclusive client access be reasonable to prevent this?

Yes, it dropped by recommendation of Greg KH <gregkh@linuxfoundation.org>. 
Uer app should care about it.

> 
> -Chip

Thanks for review.
Oleksandr.
Oleksandr Shamray Nov. 14, 2017, 10:34 a.m. | #4
> -----Original Message-----
> From: Chip Bilbrey [mailto:chip@bilbrey.org]
> Sent: Monday, November 6, 2017 12:33 AM
> To: Oleksandr Shamray <oleksandrs@mellanox.com>
> Cc: gregkh@linuxfoundation.org; arnd@arndb.de; linux-
> kernel@vger.kernel.org; linux-arm-kernel@lists.infradead.org;
> devicetree@vger.kernel.org; openbmc@lists.ozlabs.org; joel@jms.id.au;
> jiri@resnulli.us; tklauser@distanz.ch; linux-serial@vger.kernel.org;
> mec@shout.net; Vadim Pasternak <vadimp@mellanox.com>; system-sw-low-
> level <system-sw-low-level@mellanox.com>; robh+dt@kernel.org; openocd-
> devel-owner@lists.sourceforge.net; linux-api@vger.kernel.org;
> davem@davemloft.net; mchehab@kernel.org; Jiri Pirko <jiri@mellanox.com>
> Subject: Re: [v11,1/4] drivers: jtag: Add JTAG core driver
> 
> 
> Oleksandr Shamray writes:

[..]

> I notice the single-open()-per-device lock was dropped by request in an earlier
> revision of your patches, but multiple processes trying to drive a single JTAG
> master could wreak serious havoc if transactions get interleaved. Would
> something like an added JTAG_LOCKCHAIN/UNLOCKCHAIN
> ioctl() for exclusive client access be reasonable to prevent this?
> 

Yes, it dropped by recommendation of Greg KH <gregkh@linuxfoundation.org>. 

Greg, what you can suggest about it. May be better to add again single-open()-per-device lock with right locking way like:

>if (mutex_lock_interruptible(&jtag->open_lock)) {
>	return -ERESTARTSYS;
>}
>
>if (jtag->opened) {
>	mutex_unlock(&jtag->open_lock);
>	return -EINVAL;
>}
>
>nonseekable_open(inode, file);
>file->private_data = jtag;
>jtag->opened++;
>mutex_unlock(&jtag->open_lock);
>

Thaks.

> -Chip
Greg Kroah-Hartman Nov. 14, 2017, 11:10 a.m. | #5
On Tue, Nov 14, 2017 at 10:34:49AM +0000, Oleksandr Shamray wrote:
> > -----Original Message-----
> > From: Chip Bilbrey [mailto:chip@bilbrey.org]
> > Sent: Monday, November 6, 2017 12:33 AM
> > To: Oleksandr Shamray <oleksandrs@mellanox.com>
> > Cc: gregkh@linuxfoundation.org; arnd@arndb.de; linux-
> > kernel@vger.kernel.org; linux-arm-kernel@lists.infradead.org;
> > devicetree@vger.kernel.org; openbmc@lists.ozlabs.org; joel@jms.id.au;
> > jiri@resnulli.us; tklauser@distanz.ch; linux-serial@vger.kernel.org;
> > mec@shout.net; Vadim Pasternak <vadimp@mellanox.com>; system-sw-low-
> > level <system-sw-low-level@mellanox.com>; robh+dt@kernel.org; openocd-
> > devel-owner@lists.sourceforge.net; linux-api@vger.kernel.org;
> > davem@davemloft.net; mchehab@kernel.org; Jiri Pirko <jiri@mellanox.com>
> > Subject: Re: [v11,1/4] drivers: jtag: Add JTAG core driver
> > 
> > 
> > Oleksandr Shamray writes:
> 
> [..]
> 
> > I notice the single-open()-per-device lock was dropped by request in an earlier
> > revision of your patches, but multiple processes trying to drive a single JTAG
> > master could wreak serious havoc if transactions get interleaved. Would
> > something like an added JTAG_LOCKCHAIN/UNLOCKCHAIN
> > ioctl() for exclusive client access be reasonable to prevent this?
> > 
> 
> Yes, it dropped by recommendation of Greg KH <gregkh@linuxfoundation.org>. 

I asked to drop it as you didn't even implement it to work correctly :)

> Greg, what you can suggest about it. May be better to add again single-open()-per-device lock with right locking way like:
> 
> >if (mutex_lock_interruptible(&jtag->open_lock)) {

You would stall an open?  Why not just return saying you can't do that?

Anyway, if you want to only have one access to the device at a time,
great, but do it in a way that works properly.

thanks,

greg k-h
Russell King - ARM Linux Nov. 14, 2017, 11:19 a.m. | #6
On Tue, Nov 14, 2017 at 12:10:46PM +0100, gregkh@linuxfoundation.org wrote:
> On Tue, Nov 14, 2017 at 10:34:49AM +0000, Oleksandr Shamray wrote:
> > Greg, what you can suggest about it. May be better to add again single-open()-per-device lock with right locking way like:
> > 
> > >if (mutex_lock_interruptible(&jtag->open_lock)) {
> 
> You would stall an open?  Why not just return saying you can't do that?

Greg, I think you need to look at the code again.

From the snippet in the email, this lock is not held while the device is
open, as you apparently think it is.  It's a short-term lock that is
held to ensure atomic access to the jtag->opened member, so that two
concurrent opens are unable to operate lock-step, resulting in
jtag->opened becoming 2.

The open function snippet in the email drops the lock as soon as it has
incremented jtag->opened, or encounters an error.

It seems entirely sensible, rather than using an atomic_t counter, as
it means that other openers are held off until the current opener has
either succeeded in opening the device or failed to open it.
Greg Kroah-Hartman Nov. 14, 2017, 11:31 a.m. | #7
On Tue, Nov 14, 2017 at 11:19:16AM +0000, Russell King - ARM Linux wrote:
> On Tue, Nov 14, 2017 at 12:10:46PM +0100, gregkh@linuxfoundation.org wrote:
> > On Tue, Nov 14, 2017 at 10:34:49AM +0000, Oleksandr Shamray wrote:
> > > Greg, what you can suggest about it. May be better to add again single-open()-per-device lock with right locking way like:
> > > 
> > > >if (mutex_lock_interruptible(&jtag->open_lock)) {
> > 
> > You would stall an open?  Why not just return saying you can't do that?
> 
> Greg, I think you need to look at the code again.

Heh, sorry, I probably got it wrong.  I'll be glad to review it in a
real patch when needed, but not in the middle of the merge window :)

thanks,

greg k-h

Patch

diff --git a/Documentation/ioctl/ioctl-number.txt b/Documentation/ioctl/ioctl-number.txt
index 3e3fdae..1af2508 100644
--- a/Documentation/ioctl/ioctl-number.txt
+++ b/Documentation/ioctl/ioctl-number.txt
@@ -321,6 +321,8 @@  Code  Seq#(hex)	Include File		Comments
 0xB0	all	RATIO devices		in development:
 					<mailto:vgo@ratio.de>
 0xB1	00-1F	PPPoX			<mailto:mostrows@styx.uwaterloo.ca>
+0xB2	00-0f	linux/jtag.h		JTAG driver
+					<mailto:oleksandrs@mellanox.com>
 0xB3	00	linux/mmc/ioctl.h
 0xB4	00-0F	linux/gpio.h		<mailto:linux-gpio@vger.kernel.org>
 0xB5	00-0F	uapi/linux/rpmsg.h	<mailto:linux-remoteproc@vger.kernel.org>
diff --git a/MAINTAINERS b/MAINTAINERS
index 205d397..dfcf49c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7292,6 +7292,16 @@  L:	linux-serial@vger.kernel.org
 S:	Maintained
 F:	drivers/tty/serial/jsm/
 
+JTAG SUBSYSTEM
+M:	Oleksandr Shamray <oleksandrs@mellanox.com>
+M:	Vadim Pasternak <vadimp@mellanox.com>
+S:	Maintained
+F:	include/linux/jtag.h
+F:	include/uapi/linux/jtag.h
+F:	drivers/jtag/
+F:	Documentation/devicetree/bindings/jtag/
+F:	Documentation/ABI/testing/jtag-cdev
+
 K10TEMP HARDWARE MONITORING DRIVER
 M:	Clemens Ladisch <clemens@ladisch.de>
 L:	linux-hwmon@vger.kernel.org
diff --git a/drivers/Kconfig b/drivers/Kconfig
index 505c676..2214678 100644
--- a/drivers/Kconfig
+++ b/drivers/Kconfig
@@ -208,4 +208,6 @@  source "drivers/tee/Kconfig"
 
 source "drivers/mux/Kconfig"
 
+source "drivers/jtag/Kconfig"
+
 endmenu
diff --git a/drivers/Makefile b/drivers/Makefile
index dfdcda0..6a2059b 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -182,3 +182,4 @@  obj-$(CONFIG_FPGA)		+= fpga/
 obj-$(CONFIG_FSI)		+= fsi/
 obj-$(CONFIG_TEE)		+= tee/
 obj-$(CONFIG_MULTIPLEXER)	+= mux/
+obj-$(CONFIG_JTAG)		+= jtag/
diff --git a/drivers/jtag/Kconfig b/drivers/jtag/Kconfig
new file mode 100644
index 0000000..0fad1a3
--- /dev/null
+++ b/drivers/jtag/Kconfig
@@ -0,0 +1,16 @@ 
+menuconfig JTAG
+	tristate "JTAG support"
+	---help---
+	  This provides basic core functionality support for jtag class devices
+	  Hardware equipped with JTAG microcontroller which can be built
+	  on top of this drivers. Driver exposes the set of IOCTL to the
+	  user space for:
+	  SIR (Scan Instruction Register, IEEE 1149.1 Data Register scan);
+	  SDR (Scan Data Register, IEEE 1149.1 Instruction Register scan);
+	  RUNTEST (Forces IEEE 1149.1 bus to a run state for specified
+	  number of clocks).
+
+	  If you want this support, you should say Y here.
+
+	  To compile this driver as a module, choose M here: the module will
+	  be called jtag.
diff --git a/drivers/jtag/Makefile b/drivers/jtag/Makefile
new file mode 100644
index 0000000..af37493
--- /dev/null
+++ b/drivers/jtag/Makefile
@@ -0,0 +1 @@ 
+obj-$(CONFIG_JTAG)		+= jtag.o
diff --git a/drivers/jtag/jtag.c b/drivers/jtag/jtag.c
new file mode 100644
index 0000000..4e68cc9
--- /dev/null
+++ b/drivers/jtag/jtag.c
@@ -0,0 +1,267 @@ 
+/*
+ * drivers/jtag/jtag.c
+ *
+ * Copyright (c) 2017 Mellanox Technologies. All rights reserved.
+ * Copyright (c) 2017 Oleksandr Shamray <oleksandrs@mellanox.com>
+ *
+ * Released under the GPLv2 only.
+ * SPDX-License-Identifier: GPL-2.0
+ */
+
+#include <linux/cdev.h>
+#include <linux/device.h>
+#include <linux/jtag.h>
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/miscdevice.h>
+#include <linux/module.h>
+#include <linux/rtnetlink.h>
+#include <linux/spinlock.h>
+#include <linux/types.h>
+#include <uapi/linux/jtag.h>
+
+#define JTAG_NAME	"jtag0"
+#define MAX_JTAG_NAME_LEN (sizeof("jtag") + 5)
+
+struct jtag {
+	struct miscdevice miscdev;
+	struct device *dev;
+	const struct jtag_ops *ops;
+	int id;
+	unsigned long priv[0];
+};
+
+static DEFINE_IDA(jtag_ida);
+
+void *jtag_priv(struct jtag *jtag)
+{
+	return jtag->priv;
+}
+EXPORT_SYMBOL_GPL(jtag_priv);
+
+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 = jtag->ops->freq_get(jtag, &value);
+		else
+			err = -EOPNOTSUPP;
+		if (err)
+			break;
+
+		if (put_user(value, (__u32 *)arg))
+			err = -EFAULT;
+		break;
+
+	case JTAG_SIOCFREQ:
+		if (get_user(value, (__u32 *)arg))
+			return -EFAULT;
+		if (value == 0)
+			return -EINVAL;
+
+		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 -EFAULT;
+
+		if (idle.mode > JTAG_XFER_SW_MODE)
+			return -EINVAL;
+
+		if (idle.endstate > JTAG_STATE_PAUSEDR)
+			return -EINVAL;
+
+		if (jtag->ops->idle)
+			err = jtag->ops->idle(jtag, &idle);
+		else
+			err = -EOPNOTSUPP;
+		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 -EINVAL;
+
+		if (xfer.mode > JTAG_XFER_SW_MODE)
+			return -EINVAL;
+
+		if (xfer.type > JTAG_SDR_XFER)
+			return -EINVAL;
+
+		if (xfer.direction > JTAG_WRITE_XFER)
+			return -EINVAL;
+
+		if (xfer.endstate > JTAG_STATE_PAUSEDR)
+			return -EINVAL;
+
+		data_size = DIV_ROUND_UP(xfer.length, BITS_PER_BYTE);
+		xfer_data = memdup_user(u64_to_user_ptr(xfer.tdio), data_size);
+
+		if (!xfer_data)
+			return -EFAULT;
+
+		if (jtag->ops->xfer) {
+			err = jtag->ops->xfer(jtag, &xfer, xfer_data);
+		} else {
+			kfree(xfer_data);
+			return -EOPNOTSUPP;
+		}
+
+		if (err) {
+			kfree(xfer_data);
+			return -EFAULT;
+		}
+
+		err = copy_to_user(u64_to_user_ptr(xfer.tdio),
+				   (void *)(xfer_data), data_size);
+
+		if (err) {
+			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);
+		if (err)
+			err = -EFAULT;
+		break;
+
+	default:
+		return -EINVAL;
+	}
+	return err;
+}
+
+static int jtag_open(struct inode *inode, struct file *file)
+{
+	struct jtag *jtag = container_of(file->private_data, struct jtag,
+					 miscdev);
+
+	file->private_data = jtag;
+	return 0;
+}
+
+static int jtag_release(struct inode *inode, struct file *file)
+{
+	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) + round_up(priv_size, ARCH_DMA_MINALIGN),
+		       GFP_KERNEL);
+	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;
+
+	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;
+
+err_jtag_name:
+	kfree(name);
+err_jtag_alloc:
+	ida_simple_remove(&jtag_ida, id);
+	return err;
+}
+EXPORT_SYMBOL_GPL(jtag_register);
+
+void jtag_unregister(struct jtag *jtag)
+{
+	misc_deregister(&jtag->miscdev);
+	kfree(jtag->miscdev.name);
+	ida_simple_remove(&jtag_ida, jtag->id);
+}
+EXPORT_SYMBOL_GPL(jtag_unregister);
+
+static void __exit jtag_exit(void)
+{
+	ida_destroy(&jtag_ida);
+}
+
+module_exit(jtag_exit);
+
+MODULE_AUTHOR("Oleksandr Shamray <oleksandrs@mellanox.com>");
+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..076198b
--- /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@mellanox.com>
+ *
+ * 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, u8 *xfer_data);
+};
+
+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..0b25a83
--- /dev/null
+++ b/include/uapi/linux/jtag.h
@@ -0,0 +1,117 @@ 
+/*
+ * JTAG class driver
+ *
+ * Copyright (c) 2017 Mellanox Technologies. All rights reserved.
+ * Copyright (c) 2017 Oleksandr Shamray <oleksandrs@mellanox.com>
+ *
+ * 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
+
+#include <linux/types.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;
+};
+
+/* ioctl interface */
+#define __JTAG_IOCTL_MAGIC	0xb2
+
+#define JTAG_IOCRUNTEST	_IOW(__JTAG_IOCTL_MAGIC, 0,\
+			     struct jtag_run_test_idle)
+#define JTAG_SIOCFREQ	_IOW(__JTAG_IOCTL_MAGIC, 1, unsigned int)
+#define JTAG_GIOCFREQ	_IOR(__JTAG_IOCTL_MAGIC, 2, unsigned int)
+#define JTAG_IOCXFER	_IOWR(__JTAG_IOCTL_MAGIC, 3, struct jtag_xfer)
+#define JTAG_GIOCSTATUS _IOWR(__JTAG_IOCTL_MAGIC, 4, enum jtag_endstate)
+
+#define JTAG_FIRST_MINOR 0
+#define JTAG_MAX_DEVICES 32
+
+#endif /* __UAPI_LINUX_JTAG_H */