cb9e84c412
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>
99 lines
3.6 KiB
Text
99 lines
3.6 KiB
Text
The Intel MID PTI project is HW implemented in Intel Atom
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system-on-a-chip designs based on the Parallel Trace
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Interface for MIPI P1149.7 cJTAG standard. The kernel solution
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for this platform involves the following files:
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./include/linux/pti.h
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./drivers/.../n_tracesink.h
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./drivers/.../n_tracerouter.c
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./drivers/.../n_tracesink.c
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./drivers/.../pti.c
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pti.c is the driver that enables various debugging features
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popular on platforms from certain mobile manufacturers.
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n_tracerouter.c and n_tracesink.c allow extra system information to
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be collected and routed to the pti driver, such as trace
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debugging data from a modem. Although n_tracerouter
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and n_tracesink are a part of the complete PTI solution,
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these two line disciplines can work separately from
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pti.c and route any data stream from one /dev/tty node
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to another /dev/tty node via kernel-space. This provides
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a stable, reliable connection that will not break unless
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the user-space application shuts down (plus avoids
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kernel->user->kernel context switch overheads of routing
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data).
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An example debugging usage for this driver system:
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*Hook /dev/ttyPTI0 to syslogd. Opening this port will also start
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a console device to further capture debugging messages to PTI.
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*Hook /dev/ttyPTI1 to modem debugging data to write to PTI HW.
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This is where n_tracerouter and n_tracesink are used.
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*Hook /dev/pti to a user-level debugging application for writing
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to PTI HW.
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*Use mipi_* Kernel Driver API in other device drivers for
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debugging to PTI by first requesting a PTI write address via
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mipi_request_masterchannel(1).
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Below is example pseudo-code on how a 'privileged' application
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can hook up n_tracerouter and n_tracesink to any tty on
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a system. 'Privileged' means the application has enough
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privileges to successfully manipulate the ldisc drivers
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but is not just blindly executing as 'root'. Keep in mind
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the use of ioctl(,TIOCSETD,) is not specific to the n_tracerouter
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and n_tracesink line discpline drivers but is a generic
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operation for a program to use a line discpline driver
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on a tty port other than the default n_tty.
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/////////// To hook up n_tracerouter and n_tracesink /////////
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// Note that n_tracerouter depends on n_tracesink.
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#include <errno.h>
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#define ONE_TTY "/dev/ttyOne"
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#define TWO_TTY "/dev/ttyTwo"
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// needed global to hand onto ldisc connection
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static int g_fd_source = -1;
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static int g_fd_sink = -1;
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// these two vars used to grab LDISC values from loaded ldisc drivers
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// in OS. Look at /proc/tty/ldiscs to get the right numbers from
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// the ldiscs loaded in the system.
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int source_ldisc_num, sink_ldisc_num = -1;
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int retval;
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g_fd_source = open(ONE_TTY, O_RDWR); // must be R/W
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g_fd_sink = open(TWO_TTY, O_RDWR); // must be R/W
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if (g_fd_source <= 0) || (g_fd_sink <= 0) {
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// doubt you'll want to use these exact error lines of code
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printf("Error on open(). errno: %d\n",errno);
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return errno;
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}
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retval = ioctl(g_fd_sink, TIOCSETD, &sink_ldisc_num);
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if (retval < 0) {
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printf("Error on ioctl(). errno: %d\n", errno);
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return errno;
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}
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retval = ioctl(g_fd_source, TIOCSETD, &source_ldisc_num);
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if (retval < 0) {
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printf("Error on ioctl(). errno: %d\n", errno);
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return errno;
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}
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/////////// To disconnect n_tracerouter and n_tracesink ////////
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// First make sure data through the ldiscs has stopped.
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// Second, disconnect ldiscs. This provides a
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// little cleaner shutdown on tty stack.
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sink_ldisc_num = 0;
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source_ldisc_num = 0;
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ioctl(g_fd_uart, TIOCSETD, &sink_ldisc_num);
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ioctl(g_fd_gadget, TIOCSETD, &source_ldisc_num);
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// Three, program closes connection, and cleanup:
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close(g_fd_uart);
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close(g_fd_gadget);
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g_fd_uart = g_fd_gadget = NULL;
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