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