Re: [patch v22 4/4] Documentation: jtag: Add ABI documentation

[Randy Dunlap]

On 05/28/2018 05:00 AM, Oleksandr Shamray wrote:
> Added document that describe the ABI for JTAG class drivrer
> 
> Signed-off-by: Oleksandr Shamray <oleksandrs@xxxxxxxxxxxx>
> Acked-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---

> ---
>  Documentation/ABI/testing/jtag-dev |   27 +++++++++
>  Documentation/jtag/overview        |   28 +++++++++
>  Documentation/jtag/transactions    |  109 ++++++++++++++++++++++++++++++++++++
>  MAINTAINERS                        |    1 +
>  4 files changed, 165 insertions(+), 0 deletions(-)
>  create mode 100644 Documentation/ABI/testing/jtag-dev
>  create mode 100644 Documentation/jtag/overview
>  create mode 100644 Documentation/jtag/transactions
> 

> diff --git a/Documentation/jtag/overview b/Documentation/jtag/overview
> new file mode 100644
> index 0000000..42b487a
> --- /dev/null
> +++ b/Documentation/jtag/overview
> @@ -0,0 +1,28 @@
> +Linux kernel JTAG support
> +=========================
> +
> +The JTAG is an industry standard for verifying hardware.

JTAG is an

> +JTAG provides access to many logic signals of a complex integrated circuit,
> +including the device pins.
> +
> +A JTAG interface is a special interface added to a chip.
> +Depending on the version of JTAG, two, four, or five pins are added.
> +
> +The connector pins are:
> +	TDI (Test Data In)
> +	TDO (Test Data Out)
> +	TCK (Test Clock)
> +	TMS (Test Mode Select)
> +	TRST (Test Reset) optional
> +
> +JTAG interface is designed to have two parts - basic core driver and
> +hardware specific driver. The basic driver introduces a general interface
> +which is not dependent of specific hardware. It provides communication
> +between user space and hardware specific driver.
> +Each JTAG device is represented as a char device from (jtag0, jtag1, ...).
> +Access to a JTAG device is performed through IOCTL calls.
> +
> +Call flow example:
> +User: open  -> /dev/jatgX
> +User: ioctl -> /dev/jtagX -> JTAG core driver -> JTAG hardware specific driver
> +User: close -> /dev/jatgX
> diff --git a/Documentation/jtag/transactions b/Documentation/jtag/transactions
> new file mode 100644
> index 0000000..2abf833
> --- /dev/null
> +++ b/Documentation/jtag/transactions
> @@ -0,0 +1,109 @@
> +The JTAG API
> +=============
> +
> +JTAG master devices can be accessed through a character misc-device.
> +Each JTAG master interface can be accessed by using /dev/jtagN.
> +
> +JTAG system calls set:
> +- SIR (Scan Instruction Register, IEEE 1149.1 Instruction Register scan);
> +- SDR (Scan Data Register, IEEE 1149.1 Data Register scan);
> +- RUNTEST (Forces the IEEE 1149.1 bus to a run state for a specified
> +number of clocks.
> +
> +open(), close()
> +-------
> +open() opens JTAG device. Only one open operation per JTAG device
> +can be performed. Two or more open for one device will return error.
> +
> +Open/Close  device:
> +- jtag_fd = open("/dev/jtag0", O_RDWR);
> +- close(jtag_fd);
> +
> +ioctl()
> +-------
> +All access operations to JTAG devices performed through ioctl interface.

                         to JTAG devices are performed through

> +The IOCTL interface supports these requests:
> +	JTAG_IOCRUNTEST - Force JTAG state machine to RUN_TEST/IDLE state
> +	JTAG_SIOCFREQ - Set JTAG TCK frequency
> +	JTAG_GIOCFREQ - Get JTAG TCK frequency
> +	JTAG_IOCXFER - send JTAG data Xfer
> +	JTAG_GIOCSTATUS - get current JTAG TAP status
> +	JTAG_SIOCMODE - set JTAG mode flags.
> +
> +JTAG_SIOCFREQ, JTAG_GIOCFREQ
> +------
> +Set/Get JTAG clock speed:
> +
> +	unsigned int jtag_fd;
> +	ioctl(jtag_fd, JTAG_SIOCFREQ, &frq);
> +	ioctl(jtag_fd, JTAG_GIOCFREQ, &frq);
> +
> +JTAG_IOCRUNTEST
> +------
> +Force JTAG state machine to RUN_TEST/IDLE state
> +
> +struct jtag_run_test_idle {
> +	__u8	reset;
> +	__u8	endstate;
> +	__u8	tck;
> +};
> +
> +reset: 0 - run IDLE/PAUSE from current state
> +	   1 - go through TEST_LOGIC/RESET state before  IDLE/PAUSE

	                                         before IDLE/PAUSE


> +endstate: completion flag
> +tck: clock counter
> +
> +Example:
> +	struct jtag_run_test_idle runtest;
> +
> +	runtest.endstate = JTAG_STATE_IDLE;
> +	runtest.reset = 0;
> +	runtest.tck = data_p->tck;
> +	usleep(25 * 1000);
> +	ioctl(jtag_fd, JTAG_IOCRUNTEST, &runtest);
> +
> +JTAG_IOCXFER
> +------
> +Send SDR/SIR transaction
> +
> +struct jtag_xfer {
> +	__u8	type;
> +	__u8	direction;
> +	__u8	endstate;
> +	__u8	padding;
> +	__u32	length;
> +	__u64	tdio;
> +};
> +
> +type: transfer type - JTAG_SIR_XFER/JTAG_SDR_XFER
> +direction: xfer direction - JTAG_SIR_XFER/JTAG_SDR_XFER,

              drop ending comma                           ^

> +length: xfer data len in bits

s/len/length/

> +tdio : xfer data array
> +endstate: xfer end state after transaction finish
> +	   can be: JTAG_STATE_IDLE/JTAG_STATE_PAUSEIR/JTAG_STATE_PAUSEDR
> +
> +Example:
> +	struct jtag_xfer xfer;
> +	static char buf[64];
> +	static unsigned int buf_len = 0;
> +	[...]
> +	xfer.type = JTAG_SDR_XFER;
> +	xfer.tdio = (__u64)buf;
> +	xfer.length = buf_len;
> +	xfer.endstate = JTAG_STATE_IDLE;
> +
> +	if (is_read)
> +		xfer.direction = JTAG_READ_XFER;
> +	else
> +		xfer.direction = JTAG_WRITE_XFER;
> +
> +	ioctl(jtag_fd, JTAG_IOCXFER, &xfer);
> +
> +JTAG_SIOCMODE
> +------
> +If hardware driver can support different running modes you can change it.
> +
> +Example:
> +	unsigned int mode;
> +	mode = JTAG_XFER_HW_MODE;
> +	ioctl(jtag_fd, JTAG_SIOCMODE, &mode);


-- 
~Randy