[PATCH v3 2/4] switchtec: Add user interface documentation

From: Logan Gunthorpe
Date: Thu Feb 23 2017 - 19:18:17 EST

This adds standard documentation for the sysfs switchtec attributes and
a RST formatted text file which documents the char device interface.
Jonathan Corbet has indicated he will move this to a new user-space
developer documentation book once it's created.

Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Signed-off-by: Stephen Bates <stephen.bates@xxxxxxxxxxxxx>
Tested-by: Krishna Dhulipala <krishnad@xxxxxx>
Reviewed-by: Wei Zhang <wzhang@xxxxxx>
Reviewed-by: Jens Axboe <axboe@xxxxxx>
Documentation/switchtec.txt | 53 +++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 54 insertions(+)
create mode 100644 Documentation/switchtec.txt

diff --git a/Documentation/switchtec.txt b/Documentation/switchtec.txt
new file mode 100644
index 0000000..4bced4c
--- /dev/null
+++ b/Documentation/switchtec.txt
@@ -0,0 +1,53 @@
+Linux Switchtec Support
+Microsemi's "Switchtec" line of PCI switch devices is already
+supported by the kernel with standard PCI switch drivers. However, the
+Switchtec device advertises a special management endpoint which
+enables some additional functionality. This includes:
+* Packet and Byte Counters
+* Firmware Upgrades
+* Event and Error logs
+* Querying port link status
+* Custom user firmware commands
+The switchtec kernel module implements this functionality.
+The primary means of communicating with the Switchtec management firmware is
+through the Memory-mapped Remote Procedure Call (MRPC) interface.
+Commands are submitted to the interface with a 4-byte command
+identifier and up to 1KB of command specific data. The firmware will
+respond with a 4 bytes return code and up to 1KB of command specific
+data. The interface only processes a single command at a time.
+Userspace Interface
+The MRPC interface will be exposed to userspace through a simple char
+device: /dev/switchtec#, one for each management endpoint in the system.
+The char device has the following semantics:
+* A write must consist of at least 4 bytes and no more than 1028 bytes.
+ The first four bytes will be interpreted as the command to run and
+ the remainder will be used as the input data. A write will send the
+ command to the firmware to begin processing.
+* Each write must be followed by exactly one read. Any double write will
+ produce an error and any read that doesn't follow a write will
+ produce an error.
+* A read will block until the firmware completes the command and return
+ the four bytes of status plus up to 1024 bytes of output data. (The
+ length will be specified by the size parameter of the read call --
+ reading less than 4 bytes will produce an error.
+* The poll call will also be supported for userspace applications that
+ need to do other things while waiting for the command to complete.
index a57686f..aa702b0 100644
@@ -9512,6 +9512,7 @@ M: Stephen Bates <stephen.bates@xxxxxxxxxxxxx>
M: Logan Gunthorpe <logang@xxxxxxxxxxxx>
L: linux-pci@xxxxxxxxxxxxxxx
S: Maintained
+F: Documentation/switchtec.txt
F: drivers/pci/switch/switchtec*