linux/Documentation/pti/pti_intel_mid.txt
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   1The Intel MID PTI project is HW implemented in Intel Atom
   2system-on-a-chip designs based on the Parallel Trace
   3Interface for MIPI P1149.7 cJTAG standard.  The kernel solution
   4for this platform involves the following files:
   5
   6./include/linux/pti.h
   7./drivers/.../n_tracesink.h
   8./drivers/.../n_tracerouter.c
   9./drivers/.../n_tracesink.c
  10./drivers/.../pti.c
  11
  12pti.c is the driver that enables various debugging features
  13popular on platforms from certain mobile manufacturers.
  14n_tracerouter.c and n_tracesink.c allow extra system information to
  15be collected and routed to the pti driver, such as trace
  16debugging data from a modem.  Although n_tracerouter
  17and n_tracesink are a part of the complete PTI solution,
  18these two line disciplines can work separately from
  19pti.c and route any data stream from one /dev/tty node
  20to another /dev/tty node via kernel-space.  This provides
  21a stable, reliable connection that will not break unless
  22the user-space application shuts down (plus avoids
  23kernel->user->kernel context switch overheads of routing
  24data).
  25
  26An example debugging usage for this driver system:
  27   *Hook /dev/ttyPTI0 to syslogd.  Opening this port will also start
  28    a console device to further capture debugging messages to PTI.
  29   *Hook /dev/ttyPTI1 to modem debugging data to write to PTI HW.
  30    This is where n_tracerouter and n_tracesink are used.
  31   *Hook /dev/pti to a user-level debugging application for writing
  32    to PTI HW.
  33   *Use mipi_* Kernel Driver API in other device drivers for
  34    debugging to PTI by first requesting a PTI write address via
  35    mipi_request_masterchannel(1).
  36
  37Below is example pseudo-code on how a 'privileged' application
  38can hook up n_tracerouter and n_tracesink to any tty on
  39a system.  'Privileged' means the application has enough
  40privileges to successfully manipulate the ldisc drivers
  41but is not just blindly executing as 'root'. Keep in mind
  42the use of ioctl(,TIOCSETD,) is not specific to the n_tracerouter
  43and n_tracesink line discpline drivers but is a generic
  44operation for a program to use a line discpline driver
  45on a tty port other than the default n_tty.
  46
  47/////////// To hook up n_tracerouter and n_tracesink /////////
  48
  49// Note that n_tracerouter depends on n_tracesink.
  50#include <errno.h>
  51#define ONE_TTY "/dev/ttyOne"
  52#define TWO_TTY "/dev/ttyTwo"
  53
  54// needed global to hand onto ldisc connection
  55static int g_fd_source = -1;
  56static int g_fd_sink  = -1;
  57
  58// these two vars used to grab LDISC values from loaded ldisc drivers
  59// in OS.  Look at /proc/tty/ldiscs to get the right numbers from
  60// the ldiscs loaded in the system.
  61int source_ldisc_num, sink_ldisc_num = -1;
  62int retval;
  63
  64g_fd_source = open(ONE_TTY, O_RDWR); // must be R/W
  65g_fd_sink   = open(TWO_TTY, O_RDWR); // must be R/W
  66
  67if (g_fd_source <= 0) || (g_fd_sink <= 0) {
  68   // doubt you'll want to use these exact error lines of code
  69   printf("Error on open(). errno: %d\n",errno);
  70   return errno;
  71}
  72
  73retval = ioctl(g_fd_sink, TIOCSETD, &sink_ldisc_num);
  74if (retval < 0) {
  75   printf("Error on ioctl().  errno: %d\n", errno);
  76   return errno;
  77}
  78
  79retval = ioctl(g_fd_source, TIOCSETD, &source_ldisc_num);
  80if (retval < 0) {
  81   printf("Error on ioctl().  errno: %d\n", errno);
  82   return errno;
  83}
  84
  85/////////// To disconnect n_tracerouter and n_tracesink ////////
  86
  87// First make sure data through the ldiscs has stopped.
  88
  89// Second, disconnect ldiscs.  This provides a
  90// little cleaner shutdown on tty stack.
  91sink_ldisc_num = 0;
  92source_ldisc_num = 0;
  93ioctl(g_fd_uart, TIOCSETD, &sink_ldisc_num);
  94ioctl(g_fd_gadget, TIOCSETD, &source_ldisc_num);
  95
  96// Three, program closes connection, and cleanup:
  97close(g_fd_uart);
  98close(g_fd_gadget);
  99g_fd_uart = g_fd_gadget = NULL;
 100
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