[patch v20 4/4] Documentation: jtag: Add ABI documentation
From: Oleksandr Shamray
Date: Mon May 14 2018 - 12:20:19 EST
Added document that describe the ABI for JTAG class drivrer
Signed-off-by: Oleksandr Shamray <oleksandrs@xxxxxxxxxxxx>
Acked-by: Arnd Bergmann <arnd@xxxxxxxx>
---
v19->v20
Comments pointed by Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
- Fix JTAG doccumentation
v18->v19
Pavel Machek <pavel@xxxxxx>
- Added JTAG doccumentation to Documentation/jtag
v17->v18
v16->v17
v15->v16
v14->v15
v13->v14
v12->v13
v11->v12
Tobias Klauser <tklauser@xxxxxxxxxx>
- rename /Documentation/ABI/testing/jatg-dev -> jtag-dev
- Typo: s/interfase/interface
v10->v11
v9->v10
Fixes added by Oleksandr:
- change jtag-cdev to jtag-dev in documentation
- update Kernel Version and Date in jtag-dev documentation;
v8->v9
v7->v8
v6->v7
Comments pointed by Pavel Machek <pavel@xxxxxx>
- Added jtag-cdev documentation to Documentation/ABI/testing folder
---
Documentation/ABI/testing/jtag-dev | 27 +++++++++
Documentation/jtag/overview | 28 +++++++++
Documentation/jtag/transactions | 109 ++++++++++++++++++++++++++++++++++++
3 files changed, 164 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/ABI/testing/jtag-dev b/Documentation/ABI/testing/jtag-dev
new file mode 100644
index 0000000..4325316
--- /dev/null
+++ b/Documentation/ABI/testing/jtag-dev
@@ -0,0 +1,27 @@
+What: /dev/jtag[0-9]+
+Date: May 2018
+KernelVersion: 4.18
+Contact: oleksandrs@xxxxxxxxxxxx
+Description:
+ The misc device files /dev/jtag* are the interface
+ between JTAG master interface and userspace.
+
+ The ioctl(2)-based ABI is defined and documented in
+ [include/uapi]<linux/jtag.h>.
+
+ The following file operations are supported:
+
+ open(2)
+ The argument flag currently support only one access
+ mode O_RDWR.
+
+ ioctl(2)
+ Initiate various actions.
+ See the inline documentation in [include/uapi]<linux/jtag.h>
+ for descriptions of all ioctls.
+
+ close(2)
+ Stops and free up the I/O contexts that was associated
+ with the file descriptor.
+
+Users: TBD
diff --git a/Documentation/jtag/overview b/Documentation/jtag/overview
new file mode 100644
index 0000000..a86f188
--- /dev/null
+++ b/Documentation/jtag/overview
@@ -0,0 +1,28 @@
+Linux kernel JTAG support
+=========================
+
+The JTAG is an industry standard for verifying hardware
+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 hw specific driver
+User: close -> /dev/jatgX
diff --git a/Documentation/jtag/transactions b/Documentation/jtag/transactions
new file mode 100644
index 0000000..6a857c8
--- /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:
+- open("/dev/jtag0", O_RDWR);
+- close(jtag_fd');
+
+ioctl()
+-------
+All access operations to JTAG devices performed through ioctl interface.
+The IOCTL interface supports this 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
+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,
+length: xfer data len in bits
+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 hw 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);
--
1.7.1