Documentation/trace/stm.rst

1 .. SPDX-License-Identifier: GPL-2.0
9 protocol multiplexing data from multiple trace sources, each one of
10 which is assigned a unique pair of master and channel. While some of
14 master/channel combination from this pool.
17 sources can only be identified by master/channel combination, so in
20 master/channel pairs to the trace sources that it understands.
23 master 7 channel 15, while arbitrary user applications can use masters
34 associated with it, located in "stp-policy" subsystem directory in
40 	$ ls /config/stp-policy/dummy_stm.my-policy/user
42 	$ cat /config/stp-policy/dummy_stm.my-policy/user/masters
44 	$ cat /config/stp-policy/dummy_stm.my-policy/user/channels
48 masters 48 through 63 and channel allocation pool has channels 0
51 channel from within these ranges.
53 These rules can be nested, for example, one can define a rule "dummy"
68 task's name (e.g., "syslogd") and if one exists, it will be used.
70 catch-all entry "default" will be used, if it exists. This entry also
79 master/channel range. The new requirement for a policy node to exist
81 and have better control over the un-identified sources.
83 Some STM devices may allow direct mapping of the channel mmio regions
84 to userspace for zero-copy writing. One mappable page (in terms of
88 stm device's channel mmio region is 64 bytes and hardware page size is
90 width==64, you should be able to mmap() one page on this file
99 For kernel-based trace sources, there is "stm_source" device
114 used to allocate master and channel numbers. If there's no such policy
115 node, the stm core will use the catch-all entry "default", if one
122 One implementation of this interface also used in the example above is
123 the "stm_console" driver, which basically provides a one-way console
126 To configure the master/channel pair that will be assigned to this
129 consume one channel.
142 * [1] https://software.intel.com/sites/default/files/managed/d3/3c/intel-th-developer-manual.pdf