path: root/Documentation/pti
diff options
authorJ Freyensee <james_p_freyensee@linux.intel.com>2011-05-06 16:56:48 -0700
committerGreg Kroah-Hartman <gregkh@suse.de>2011-05-13 16:31:00 -0700
commitcb9e84c4123088f4641009f5217b7d32b307992f (patch)
tree09197e3d4bb821b3c5d545fd0443f376a21158f6 /Documentation/pti
parent7d74f492e4dd0034a61458eb80f70b1d2862ed07 (diff)
Kernel documentation for the PTI feature.
This provides Kernel documentation for the PTI feature and setting line discipline drivers on top of tty's for Linux mobile solutions. Signed-off-by: J Freyensee <james_p_freyensee@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'Documentation/pti')
1 files changed, 99 insertions, 0 deletions
diff --git a/Documentation/pti/pti_intel_mid.txt b/Documentation/pti/pti_intel_mid.txt
new file mode 100644
index 00000000000..e7a5b6d1f7a
--- /dev/null
+++ b/Documentation/pti/pti_intel_mid.txt
@@ -0,0 +1,99 @@
+The Intel MID PTI project is HW implemented in Intel Atom
+system-on-a-chip designs based on the Parallel Trace
+Interface for MIPI P1149.7 cJTAG standard. The kernel solution
+for this platform involves the following files:
+pti.c is the driver that enables various debugging features
+popular on platforms from certain mobile manufacturers.
+n_tracerouter.c and n_tracesink.c allow extra system information to
+be collected and routed to the pti driver, such as trace
+debugging data from a modem. Although n_tracerouter
+and n_tracesink are a part of the complete PTI solution,
+these two line disciplines can work separately from
+pti.c and route any data stream from one /dev/tty node
+to another /dev/tty node via kernel-space. This provides
+a stable, reliable connection that will not break unless
+the user-space application shuts down (plus avoids
+kernel->user->kernel context switch overheads of routing
+An example debugging usage for this driver system:
+ *Hook /dev/ttyPTI0 to syslogd. Opening this port will also start
+ a console device to further capture debugging messages to PTI.
+ *Hook /dev/ttyPTI1 to modem debugging data to write to PTI HW.
+ This is where n_tracerouter and n_tracesink are used.
+ *Hook /dev/pti to a user-level debugging application for writing
+ to PTI HW.
+ *Use mipi_* Kernel Driver API in other device drivers for
+ debugging to PTI by first requesting a PTI write address via
+ mipi_request_masterchannel(1).
+Below is example pseudo-code on how a 'privileged' application
+can hook up n_tracerouter and n_tracesink to any tty on
+a system. 'Privileged' means the application has enough
+privileges to successfully manipulate the ldisc drivers
+but is not just blindly executing as 'root'. Keep in mind
+the use of ioctl(,TIOCSETD,) is not specific to the n_tracerouter
+and n_tracesink line discpline drivers but is a generic
+operation for a program to use a line discpline driver
+on a tty port other than the default n_tty.
+/////////// To hook up n_tracerouter and n_tracesink /////////
+// Note that n_tracerouter depends on n_tracesink.
+#include <errno.h>
+#define ONE_TTY "/dev/ttyOne"
+#define TWO_TTY "/dev/ttyTwo"
+// needed global to hand onto ldisc connection
+static int g_fd_source = -1;
+static int g_fd_sink = -1;
+// these two vars used to grab LDISC values from loaded ldisc drivers
+// in OS. Look at /proc/tty/ldiscs to get the right numbers from
+// the ldiscs loaded in the system.
+int source_ldisc_num, sink_ldisc_num = -1;
+int retval;
+g_fd_source = open(ONE_TTY, O_RDWR); // must be R/W
+g_fd_sink = open(TWO_TTY, O_RDWR); // must be R/W
+if (g_fd_source <= 0) || (g_fd_sink <= 0) {
+ // doubt you'll want to use these exact error lines of code
+ printf("Error on open(). errno: %d\n",errno);
+ return errno;
+retval = ioctl(g_fd_sink, TIOCSETD, &sink_ldisc_num);
+if (retval < 0) {
+ printf("Error on ioctl(). errno: %d\n", errno);
+ return errno;
+retval = ioctl(g_fd_source, TIOCSETD, &source_ldisc_num);
+if (retval < 0) {
+ printf("Error on ioctl(). errno: %d\n", errno);
+ return errno;
+/////////// To disconnect n_tracerouter and n_tracesink ////////
+// First make sure data through the ldiscs has stopped.
+// Second, disconnect ldiscs. This provides a
+// little cleaner shutdown on tty stack.
+sink_ldisc_num = 0;
+source_ldisc_num = 0;
+ioctl(g_fd_uart, TIOCSETD, &sink_ldisc_num);
+ioctl(g_fd_gadget, TIOCSETD, &source_ldisc_num);
+// Three, program closes connection, and cleanup:
+g_fd_uart = g_fd_gadget = NULL;