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author | J Freyensee <james_p_freyensee@linux.intel.com> | 2011-05-06 16:56:48 -0700 |
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committer | Greg Kroah-Hartman <gregkh@suse.de> | 2011-05-13 16:31:00 -0700 |
commit | cb9e84c4123088f4641009f5217b7d32b307992f (patch) | |
tree | 09197e3d4bb821b3c5d545fd0443f376a21158f6 /Documentation | |
parent | 7d74f492e4dd0034a61458eb80f70b1d2862ed07 (diff) |
Kernel documentation for the PTI feature.
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>
Diffstat (limited to 'Documentation')
-rw-r--r-- | Documentation/pti/pti_intel_mid.txt | 99 |
1 files changed, 99 insertions, 0 deletions
diff --git a/Documentation/pti/pti_intel_mid.txt b/Documentation/pti/pti_intel_mid.txt new file mode 100644 index 00000000000..e7a5b6d1f7a --- /dev/null +++ b/Documentation/pti/pti_intel_mid.txt @@ -0,0 +1,99 @@ +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; |