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switchtec: Add user interface documentation

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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>
This commit is contained in:
Logan Gunthorpe 2017-03-02 16:24:32 -07:00 committed by Bjorn Helgaas
parent 080b47def5
commit 44fc691b4f
2 changed files with 54 additions and 0 deletions
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53
Documentation/switchtec.txt Normal file
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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.

1
MAINTAINERS
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@ -9661,6 +9661,7 @@ M: Stephen Bates <stephen.bates@microsemi.com>
M: Logan Gunthorpe <logang@deltatee.com>
L: linux-pci@vger.kernel.org
S: Maintained
F: Documentation/switchtec.txt
F: drivers/pci/switch/switchtec*
PCI DRIVER FOR NVIDIA TEGRA