stm class: Introduce an abstraction for System Trace Module devices

A System Trace Module (STM) is a device exporting data in System Trace
Protocol (STP) format as defined by MIPI STP standards. Examples of such
devices are Intel(R) Trace Hub and Coresight STM.

This abstraction provides a unified interface for software trace sources
to send their data over an STM device to a debug host. In order to do
that, such a trace source needs to be assigned a pair of master/channel
identifiers that all the data from this source will be tagged with. The
STP decoder on the debug host side will use these master/channel tags to
distinguish different trace streams from one another inside one STP
stream.

This abstraction provides a configfs-based policy management mechanism
for dynamic allocation of these master/channel pairs based on trace
source-supplied string identifier. It has the flexibility of being
defined at runtime and at the same time (provided that the policy
definition is aligned with the decoding end) consistency.

For userspace trace sources, this abstraction provides write()-based and
mmap()-based (if the underlying stm device allows this) output mechanism.

For kernel-side trace sources, we provide "stm_source" device class that
can be connected to an stm device at run time.

Cc: linux-api@vger.kernel.org
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

3 files changed, 73 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/configfs-stp-policy b/Documentation/ABI/testing/configfs-stp-policy
new file mode 100644
index 0000000..421ce68
--- /dev/null
+++ b/Documentation/ABI/testing/configfs-stp-policy
@@ -0,0 +1,48 @@
+What:		/config/stp-policy
+Date:		June 2015
+KernelVersion:	4.3
+Description:
+		This group contains policies mandating Master/Channel allocation
+		for software sources wishing to send trace data over an STM
+		device.
+
+What:		/config/stp-policy/<device>.<policy>
+Date:		June 2015
+KernelVersion:	4.3
+Description:
+		This group is the root of a policy; its name is a concatenation
+		of an stm device name to which this policy applies and an
+		arbitrary string. If <device> part doesn't match an existing
+		stm device, mkdir will fail with ENODEV; if that device already
+		has a policy assigned to it, mkdir will fail with EBUSY.
+
+What:		/config/stp-policy/<device>.<policy>/device
+Date:		June 2015
+KernelVersion:	4.3
+Description:
+		STM device to which this policy applies, read only. Same as the
+		<device> component of its parent directory.
+
+What:		/config/stp-policy/<device>.<policy>/<node>
+Date:		June 2015
+KernelVersion:	4.3
+Description:
+		Policy node is a string identifier that software clients will
+		use to request a master/channel to be allocated and assigned to
+		them.
+
+What:		/config/stp-policy/<device>.<policy>/<node>/masters
+Date:		June 2015
+KernelVersion:	4.3
+Description:
+		Range of masters from which to allocate for users of this node.
+		Write two numbers: the first master and the last master number.
+
+What:		/config/stp-policy/<device>.<policy>/<node>/channels
+Date:		June 2015
+KernelVersion:	4.3
+Description:
+		Range of channels from which to allocate for users of this node.
+		Write two numbers: the first channel and the last channel
+		number.
+
diff --git a/Documentation/ABI/testing/sysfs-class-stm b/Documentation/ABI/testing/sysfs-class-stm
new file mode 100644
index 0000000..c9aa4f3
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-stm
@@ -0,0 +1,14 @@
+What:		/sys/class/stm/<stm>/masters
+Date:		June 2015
+KernelVersion:	4.3
+Contact:	Alexander Shishkin <alexander.shishkin@linux.intel.com>
+Description:
+		Shows first and last available to software master numbers on
+		this STM device.
+
+What:		/sys/class/stm/<stm>/channels
+Date:		June 2015
+KernelVersion:	4.3
+Contact:	Alexander Shishkin <alexander.shishkin@linux.intel.com>
+Description:
+		Shows the number of channels per master on this STM device.
diff --git a/Documentation/ABI/testing/sysfs-class-stm_source b/Documentation/ABI/testing/sysfs-class-stm_source
new file mode 100644
index 0000000..57b8dd3
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-stm_source
@@ -0,0 +1,11 @@
+What:		/sys/class/stm_source/<stm_source>/stm_source_link
+Date:		June 2015
+KernelVersion:	4.3
+Contact:	Alexander Shishkin <alexander.shishkin@linux.intel.com>
+Description:
+		stm_source device linkage to stm device, where its tracing data
+		is directed. Reads return an existing connection or "<none>" if
+		this stm_source is not connected to any stm device yet.
+		Write an existing (registered) stm device's name here to
+		connect that device. If a device is already connected to this
+		stm_source, it will first be disconnected.