Document the additionally provided special files and their usage in the
context of the alternative binary ioctl-based interface.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
---
 Documentation/filesystems/stlmfs.rst | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/Documentation/filesystems/stlmfs.rst b/Documentation/filesystems/stlmfs.rst
index a15da85b9971..0c7b7c006709 100644
--- a/Documentation/filesystems/stlmfs.rst
+++ b/Documentation/filesystems/stlmfs.rst
@@ -143,6 +143,7 @@ create the following directory structure::
 	|-- all_des_enable
 	|-- all_des_tstamp_enable
 	|-- available_update_intervals_ms
+	|-- control
 	|-- current_update_interval_ms
 	|-- de_implementation_version
 	|-- des/
@@ -160,6 +161,10 @@ create the following directory structure::
 	|-- tlm_enable
 	`-- version
 
+.. Note::
+	The control/ special file can be used to use the alternative
+	binary interface described in include/uapi/linux/scmi.h
+
 Each subdirectory is defined as follows.
 
 des/
@@ -220,6 +225,7 @@ values, as in::
 	scmi_tlm_0/groups/0/
 	|-- available_update_intervals_ms
 	|-- composing_des
+	|-- control
 	|-- current_update_interval_ms
 	|-- des_bulk_read
 	|-- des_single_sample_read
@@ -227,3 +233,21 @@ values, as in::
 	|-- intervals_discrete
 	`-- tstamp_enable
 
+Alternative Binary Interfaces - Special files
+=============================================
+
+Special files are populated across the filesystem so as to implement the support
+of more performant alternative binary interfaces that can be used instead of the
+main human readable ABI.
+
+IOCTLs Interface
+----------------
+
+The ioctl-based interface is detailed in::
+
+	include/uapi/linux/scmi.h
+
+The filesystem provides special files named *control/* to be used with the
+ioctl interface mentioned above: note that the behaviour of some of the ioctls
+is dependent on which *control/* file is used to invoke them (as detailed in the
+UAPI header above).
-- 
2.54.0