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Documentation / pti / pti_intel_mid.txt




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Based on kernel version 3.15.4. Page generated on 2014-07-07 09:04 EST.

1	The Intel MID PTI project is HW implemented in Intel Atom
2	system-on-a-chip designs based on the Parallel Trace
3	Interface for MIPI P1149.7 cJTAG standard.  The kernel solution
4	for 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	
12	pti.c is the driver that enables various debugging features
13	popular on platforms from certain mobile manufacturers.
14	n_tracerouter.c and n_tracesink.c allow extra system information to
15	be collected and routed to the pti driver, such as trace
16	debugging data from a modem.  Although n_tracerouter
17	and n_tracesink are a part of the complete PTI solution,
18	these two line disciplines can work separately from
19	pti.c and route any data stream from one /dev/tty node
20	to another /dev/tty node via kernel-space.  This provides
21	a stable, reliable connection that will not break unless
22	the user-space application shuts down (plus avoids
23	kernel->user->kernel context switch overheads of routing
24	data).
25	
26	An 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	
37	Below is example pseudo-code on how a 'privileged' application
38	can hook up n_tracerouter and n_tracesink to any tty on
39	a system.  'Privileged' means the application has enough
40	privileges to successfully manipulate the ldisc drivers
41	but is not just blindly executing as 'root'. Keep in mind
42	the use of ioctl(,TIOCSETD,) is not specific to the n_tracerouter
43	and n_tracesink line discpline drivers but is a generic
44	operation for a program to use a line discpline driver
45	on 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
55	static int g_fd_source = -1;
56	static 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.
61	int source_ldisc_num, sink_ldisc_num = -1;
62	int retval;
63	
64	g_fd_source = open(ONE_TTY, O_RDWR); // must be R/W
65	g_fd_sink   = open(TWO_TTY, O_RDWR); // must be R/W
66	
67	if (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	
73	retval = ioctl(g_fd_sink, TIOCSETD, &sink_ldisc_num);
74	if (retval < 0) {
75	   printf("Error on ioctl().  errno: %d\n", errno);
76	   return errno;
77	}
78	
79	retval = ioctl(g_fd_source, TIOCSETD, &source_ldisc_num);
80	if (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.
91	sink_ldisc_num = 0;
92	source_ldisc_num = 0;
93	ioctl(g_fd_uart, TIOCSETD, &sink_ldisc_num);
94	ioctl(g_fd_gadget, TIOCSETD, &source_ldisc_num);
95	
96	// Three, program closes connection, and cleanup:
97	close(g_fd_uart);
98	close(g_fd_gadget);
99	g_fd_uart = g_fd_gadget = NULL;
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