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-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:
-
-./include/linux/pti.h
-./drivers/.../n_tracesink.h
-./drivers/.../n_tracerouter.c
-./drivers/.../n_tracesink.c
-./drivers/.../pti.c
-
-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
-data).
-
-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:
-close(g_fd_uart);
-close(g_fd_gadget);
-g_fd_uart = g_fd_gadget = NULL;