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authorLogan Gunthorpe <logang@deltatee.com>2017-03-03 02:24:32 +0300
committerBjorn Helgaas <bhelgaas@google.com>2017-04-12 20:23:37 +0300
commit44fc691b4fac3aff3e99b42cad3a994f5a6621ac (patch)
tree01cbe0a250b51a82170563fd8e6c39166930e838 /Documentation/switchtec.txt
parent080b47def5e5e28b2509c5bb92160d1df730f27b (diff)
downloadlinux-44fc691b4fac3aff3e99b42cad3a994f5a6621ac.tar.xz
switchtec: Add user interface documentation
Add 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. Tested-by: Krishna Dhulipala <krishnad@fb.com> Signed-off-by: Logan Gunthorpe <logang@deltatee.com> Signed-off-by: Stephen Bates <stephen.bates@microsemi.com> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> Reviewed-by: Wei Zhang <wzhang@fb.com> Reviewed-by: Jens Axboe <axboe@fb.com>
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+========================
+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.
+
+
+Interface
+=========
+
+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.