| Logan Gunthorpe | 44fc691 | 2017-03-02 16:24:32 -0700 | [diff] [blame^] | 1 | ======================== |
| 2 | Linux Switchtec Support |
| 3 | ======================== |
| 4 | |
| 5 | Microsemi's "Switchtec" line of PCI switch devices is already |
| 6 | supported by the kernel with standard PCI switch drivers. However, the |
| 7 | Switchtec device advertises a special management endpoint which |
| 8 | enables some additional functionality. This includes: |
| 9 | |
| 10 | * Packet and Byte Counters |
| 11 | * Firmware Upgrades |
| 12 | * Event and Error logs |
| 13 | * Querying port link status |
| 14 | * Custom user firmware commands |
| 15 | |
| 16 | The switchtec kernel module implements this functionality. |
| 17 | |
| 18 | |
| 19 | Interface |
| 20 | ========= |
| 21 | |
| 22 | The primary means of communicating with the Switchtec management firmware is |
| 23 | through the Memory-mapped Remote Procedure Call (MRPC) interface. |
| 24 | Commands are submitted to the interface with a 4-byte command |
| 25 | identifier and up to 1KB of command specific data. The firmware will |
| 26 | respond with a 4 bytes return code and up to 1KB of command specific |
| 27 | data. The interface only processes a single command at a time. |
| 28 | |
| 29 | |
| 30 | Userspace Interface |
| 31 | =================== |
| 32 | |
| 33 | The MRPC interface will be exposed to userspace through a simple char |
| 34 | device: /dev/switchtec#, one for each management endpoint in the system. |
| 35 | |
| 36 | The char device has the following semantics: |
| 37 | |
| 38 | * A write must consist of at least 4 bytes and no more than 1028 bytes. |
| 39 | The first four bytes will be interpreted as the command to run and |
| 40 | the remainder will be used as the input data. A write will send the |
| 41 | command to the firmware to begin processing. |
| 42 | |
| 43 | * Each write must be followed by exactly one read. Any double write will |
| 44 | produce an error and any read that doesn't follow a write will |
| 45 | produce an error. |
| 46 | |
| 47 | * A read will block until the firmware completes the command and return |
| 48 | the four bytes of status plus up to 1024 bytes of output data. (The |
| 49 | length will be specified by the size parameter of the read call -- |
| 50 | reading less than 4 bytes will produce an error. |
| 51 | |
| 52 | * The poll call will also be supported for userspace applications that |
| 53 | need to do other things while waiting for the command to complete. |