[PATCH v3 8/8] thunderbolt: Networking doc

[Amir Levy]

Adding Thunderbolt(TM) networking documentation.

Signed-off-by: Amir Levy <amir.jer.levy@xxxxxxxxx>
---
 Documentation/00-INDEX                   |   2 +
 Documentation/thunderbolt-networking.txt | 135 +++++++++++++++++++++++++++++++
 2 files changed, 137 insertions(+)
 create mode 100644 Documentation/thunderbolt-networking.txt

diff --git a/Documentation/00-INDEX b/Documentation/00-INDEX
index cd077ca..8cf1717 100644
--- a/Documentation/00-INDEX
+++ b/Documentation/00-INDEX
@@ -439,6 +439,8 @@ this_cpu_ops.txt
 	- List rationale behind and the way to use this_cpu operations.
 thermal/
 	- directory with information on managing thermal issues (CPU/temp)
+thunderbolt-networking.txt
+	- Thunderbolt(TM) Networking driver description.
 trace/
 	- directory with info on tracing technologies within linux
 unaligned-memory-access.txt
diff --git a/Documentation/thunderbolt-networking.txt b/Documentation/thunderbolt-networking.txt
new file mode 100644
index 0000000..b7714cf
--- /dev/null
+++ b/Documentation/thunderbolt-networking.txt
@@ -0,0 +1,135 @@
+Intel Thunderbolt(TM) Linux driver
+==================================
+
+Copyright(c) 2013 - 2016 Intel Corporation.
+
+Contact Information:
+Intel Thunderbolt mailing list <thunderbolt-software@xxxxxxxxxxxx>
+Edited by Michael Jamet <michael.jamet@xxxxxxxxx>
+
+Overview
+========
+
+Thunderbolt(TM) Networking mode is introduced with this driver.
+This kernel code creates an ethernet device utilized in computer to computer
+communication over a Thunderbolt cable.
+This driver has been added on the top of the existing thunderbolt driver
+for systems with firwmare (FW) based Thunderbolt controllers supporting
+Thunderbolt Networking.
+
+Files
+=====
+
+- icm_nhi.c/h:	These files allow communication with the FW (a.k.a ICM) based controller.
+		In addition, they create an interface for netlink communication with
+		a user space daemon.
+
+- net.c/net.h:	These files implement the 'eth' interface for the Thunderbolt(TM)
+		networking.
+
+Interface to user space
+=======================
+
+The interface to the user space module is implemented through a Generic Netlink.
+In order to be accessed by the user space module, both kernel and user space
+modules have to register with the same GENL_NAME. In our case, this is
+simply "thunderbolt".
+The registration is done at driver initialization time for all instances of
+the Thunderbolt controllers.
+The communication is then carried through pre-defined Thunderbolt messages.
+Each specific message has a callback function that is called when
+the related message is received.
+
+The messages are defined as follows:
+* NHI_CMD_UNSPEC: Not used.
+* NHI_CMD_SUBSCRIBE: Subscription request from daemon to driver to open the
+  communication channel.
+* NHI_CMD_UNSUBSCRIBE: Request from daemon to driver to unsubscribe
+  to close communication channel.
+* NHI_CMD_QUERY_INFORMATION: Request information from the driver such as
+  driver version, FW version offset, number of ports in the controller
+  and DMA port.
+* NHI_CMD_MSG_TO_ICM: Message from user space module to FW.
+* NHI_CMD_MSG_FROM_ICM: Response from FW to user space module.
+* NHI_CMD_MAILBOX: Message that uses mailbox mechanism such as FW policy
+  changes or disconnect path.
+* NHI_CMD_APPROVE_TBT_NETWORKING: Request from user space
+  module to FW to establish path.
+* NHI_CMD_ICM_IN_SAFE_MODE: Indication that the FW has entered safe mode.
+
+Communication with ICM (Firmware)
+=================================
+
+The communication with ICM is principally achieved through
+a DMA mechanism on Ring 0.
+The driver allocates a shared memory that is physically mapped onto
+the DMA physical space at Ring 0.
+
+Interrupts
+==========
+
+Thunderbolt relies on MSI-X interrupts.
+The MSI-X vector is allocated as follows:
+ICM
+     - Tx: MSI-X vector index 0
+     - Rx: MSI-X vector index 1
+
+Port 0
+     - Tx: MSI-X vector index 2
+     - Rx: MSI-X vector index 3
+
+Port 1
+     - Tx: MSI-X vector index 4
+     - Rx: MSI-X vector index 5
+
+ICM interrupts are used for communication with ICM only.
+Port 0 and Port 1 interrupts are used for Thunderbolt Networking
+communications.
+In case MSI-X is not available, the driver requests to enable MSI only.
+
+Mutexes, semaphores and spinlocks
+=================================
+
+The driver should be able to operate in an environment where hardware
+is asynchronously accessed by multiple entities such as netlink,
+multiple controllers etc.
+
+* send_sem: This semaphore enforces unique sender (one sender at a time)
+  to avoid wrong impairing with responses. FW may process one message
+  at the time.
+* d0_exit_send_mutex: This mutex protects D0 exit (D3) situation
+  to avoid continuing to send messages to FW.
+* d0_exit_mailbox_mutex: This mutex protects D0 exit (D3) situation to
+  avoid continuing to send commands to mailbox.
+* mailbox_mutex: This mutex enforces unique sender (one sender at a time)
+  for the mailbox command.
+  A mutex is sufficient since the mailbox mechanism uses a polling mechanism
+  to get the command response.
+* lock: This spinlock protects from simultaneous changes during
+  disable/enable interrupts.
+* state_lock: This mutex comes to protect changes during net device state
+  changes and net_device operations.
+* controllers_list_rwsem: This read/write sempahore syncs the access to
+  the controllers list when there are multiple controllers in the system.
+
+FW path enablement
+==================
+
+In order to SW to communicate with the FW, the driver needs to send to FW
+the PDF driver ready command and receive response from FW.
+The driver ready command PDF value is 12 and the response is 13.
+Once the exchange is completed, the user space module should be able to send
+messages through the driver to the FW and FW starts to send notifications
+about HW/FW events.
+
+Information
+===========
+
+Mailing list:
+	thunderbolt-software@xxxxxxxxxxxx
+	Register at: https://lists.01.org/mailman/listinfo/thunderbolt-software
+	Archives at: https://lists.01.org/pipermail/thunderbolt-software/
+
+For additional information about Thunderbolt technology visit:
+	https://01.org/thunderbolt-sw
+	https://thunderbolttechnology.net/
-- 
2.7.4