mirror of
https://github.com/torvalds/linux.git
synced 2024-11-01 01:31:44 +00:00
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>
100 lines
3.6 KiB
Plaintext
100 lines
3.6 KiB
Plaintext
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;
|