Documentation/hwmon/sbrmi.rst

   1 .. SPDX-License-Identifier: GPL-2.0-or-later
   2
   3 Kernel driver sbrmi
   4 ===================
   5
   6 Supported hardware:
   7
   8   * Sideband Remote Management Interface (SB-RMI) compliant AMD SoC
   9     device connected to the BMC via the APML.
  10
  11     Prefix: 'sbrmi'
  12
  13     Addresses scanned: This driver doesn't support address scanning.
  14
  15     To instantiate this driver on an AMD CPU with SB-RMI
  16     support, the i2c bus number would be the bus connected from the board
  17     management controller (BMC) to the CPU.
  18     The SMBus address is really 7 bits. Some vendors and the SMBus
  19     specification show the address as 8 bits, left justified with the R/W
  20     bit as a write (0) making bit 0. Some vendors use only the 7 bits
  21     to describe the address.
  22     As mentioned in AMD's APML specification, The SB-RMI address is
  23     normally 78h(0111 100W) or 3Ch(011 1100) for socket 0 and 70h(0111 000W)
  24     or 38h(011 1000) for socket 1, but it could vary based on hardware
  25     address select pins.
  26
  27     Datasheet: The SB-RMI interface and protocol along with the Advanced
  28                Platform Management Link (APML) Specification is available
  29                as part of the open source SoC register reference at:
  30
  31                https://www.amd.com/en/support/tech-docs?keyword=55898
  32
  33 Author: Akshay Gupta <akshay.gupta@amd.com>
  34
  35 Description
  36 -----------
  37
  38 The APML provides a way to communicate with the SB Remote Management interface
  39 (SB-RMI) module from the external SMBus master that can be used to report socket
  40 power on AMD platforms using mailbox command and resembles a typical 8-pin remote
  41 power sensor's I2C interface to BMC.
  42
  43 This driver implements current power with power cap and power cap max.
  44
  45 sysfs-Interface
  46 ---------------
  47 Power sensors can be queried and set via the standard ``hwmon`` interface
  48 on ``sysfs``, under the directory ``/sys/class/hwmon/hwmonX`` for some value
  49 of ``X`` (search for the ``X`` such that ``/sys/class/hwmon/hwmonX/name`` has
  50 content ``sbrmi``)
  51
  52 ================ ===== ========================================================
  53 Name             Perm   Description
  54 ================ ===== ========================================================
  55 power1_input     RO    Current Power consumed
  56 power1_cap       RW    Power limit can be set between 0 and power1_cap_max
  57 power1_cap_max   RO    Maximum powerlimit calculated and reported by the SMU FW
  58 ================ ===== ========================================================
  59
  60 The following example show how the 'Power' attribute from the i2c-addresses
  61 can be monitored using the userspace utilities like ``sensors`` binary::
  62
  63   # sensors
  64   sbrmi-i2c-1-38
  65   Adapter: bcm2835 I2C adapter
  66   power1:       61.00 W (cap = 225.00 W)
  67
  68   sbrmi-i2c-1-3c
  69   Adapter: bcm2835 I2C adapter
  70   power1:       28.39 W (cap = 224.77 W)
  71   #
  72
  73 Also, Below shows how get and set the values from sysfs entries individually::
  74   # cat /sys/class/hwmon/hwmon1/power1_cap_max
  75   225000000
  76
  77   # echo 180000000 > /sys/class/hwmon/hwmon1/power1_cap
  78   # cat /sys/class/hwmon/hwmon1/power1_cap
  79   180000000