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hwmon: (sbrmi) Add Documentation

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- Add documentation for SB-RMI module

Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Akshay Gupta <Akshay.Gupta@amd.com>
Signed-off-by: Naveen Krishna Chatradhi <nchatrad@amd.com>
Link: https://lore.kernel.org/r/20210726133615.9709-2-nchatrad@amd.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
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Akshay Gupta 2021-07-26 19:06:14 +05:30 committed by Guenter Roeck
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commit 04165fb73f
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Documentation/hwmon/index.rst
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@ -160,6 +160,7 @@ Hardware Monitoring Kernel Drivers
pwm-fan
q54sj108a2
raspberrypi-hwmon
sbrmi
sbtsi_temp
sch5627
sch5636

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Documentation/hwmon/sbrmi.rst Normal file
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@ -0,0 +1,79 @@
.. SPDX-License-Identifier: GPL-2.0-or-later
Kernel driver sbrmi
===================
Supported hardware:
* Sideband Remote Management Interface (SB-RMI) compliant AMD SoC
device connected to the BMC via the APML.
Prefix: 'sbrmi'
Addresses scanned: This driver doesn't support address scanning.
To instantiate this driver on an AMD CPU with SB-RMI
support, the i2c bus number would be the bus connected from the board
management controller (BMC) to the CPU.
The SMBus address is really 7 bits. Some vendors and the SMBus
specification show the address as 8 bits, left justified with the R/W
bit as a write (0) making bit 0. Some vendors use only the 7 bits
to describe the address.
As mentioned in AMD's APML specification, The SB-RMI address is
normally 78h(0111 100W) or 3Ch(011 1100) for socket 0 and 70h(0111 000W)
or 38h(011 1000) for socket 1, but it could vary based on hardware
address select pins.
Datasheet: The SB-RMI interface and protocol along with the Advanced
Platform Management Link (APML) Specification is available
as part of the open source SoC register reference at:
https://www.amd.com/en/support/tech-docs?keyword=55898
Author: Akshay Gupta <akshay.gupta@amd.com>
Description
-----------
The APML provides a way to communicate with the SB Remote Management interface
(SB-RMI) module from the external SMBus master that can be used to report socket
power on AMD platforms using mailbox command and resembles a typical 8-pin remote
power sensor's I2C interface to BMC.
This driver implements current power with power cap and power cap max.
sysfs-Interface
---------------
Power sensors can be queried and set via the standard ``hwmon`` interface
on ``sysfs``, under the directory ``/sys/class/hwmon/hwmonX`` for some value
of ``X`` (search for the ``X`` such that ``/sys/class/hwmon/hwmonX/name`` has
content ``sbrmi``)
================ ===== ========================================================
Name Perm Description
================ ===== ========================================================
power1_input RO Current Power consumed
power1_cap RW Power limit can be set between 0 and power1_cap_max
power1_cap_max RO Maximum powerlimit calculated and reported by the SMU FW
================ ===== ========================================================
The following example show how the 'Power' attribute from the i2c-addresses
can be monitored using the userspace utilities like ``sensors`` binary::
# sensors
sbrmi-i2c-1-38
Adapter: bcm2835 I2C adapter
power1: 61.00 W (cap = 225.00 W)
sbrmi-i2c-1-3c
Adapter: bcm2835 I2C adapter
power1: 28.39 W (cap = 224.77 W)
#
Also, Below shows how get and set the values from sysfs entries individually::
# cat /sys/class/hwmon/hwmon1/power1_cap_max
225000000
# echo 180000000 > /sys/class/hwmon/hwmon1/power1_cap
# cat /sys/class/hwmon/hwmon1/power1_cap
180000000