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docs: misc: amd-sbi: Document SBTSI userspace interface

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- Document AMD sideband IOCTL description defined
  for SBTSI and its usage.
  User space C-APIs are made available by esmi_oob_library [1],
  which is provided by the E-SMS project [2].

  Link: https://github.com/amd/esmi_oob_library [1]
  Link: https://www.amd.com/en/developer/e-sms.html [2]

Include a user-space open example for /dev/sbtsi-* and list auxiliary
bus sysfs paths.

Reviewed-by: Akshay Gupta <Akshay.Gupta@amd.com>
Signed-off-by: Prathima <Prathima.Lk@amd.com>
Link: https://github.com/amd/esmi_oob_library [1]
Link: https://www.amd.com/en/developer/e-sms.html [2]
Link: https://patch.msgid.link/20260710111642.850022-9-Akshay.Gupta@amd.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Prathima 2026-07-10 16:46:42 +05:30 committed by Greg Kroah-Hartman
parent 47f6311f8f
commit 9bdecb9173
1 changed files with 74 additions and 0 deletions
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74
Documentation/misc-devices/amd-sbi.rst
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@ -48,6 +48,66 @@ Access restrictions:
* APML Mailbox messages and Register xfer access are read-write,
* CPUID and MCA_MSR access is read-only.
SBTSI device
============
sbtsi driver under the drivers/misc/amd-sbi creates miscdevice
/dev/sbtsi-* to let user space programs run APML TSI register transfer
commands.
The driver supports both I2C and I3C transports for SB-TSI targets.
The transport is selected by the bus where the device is enumerated.
Misc device:
* In 1P socket 0: /dev/sbtsi-4c
* In 2P socket 0: /dev/sbtsi-4c, socket 1: /dev/sbtsi-48
.. code-block:: bash
$ ls -al /dev/sbtsi-4c
crw------- 1 root root 10, 116 Apr 2 05:22 /dev/sbtsi-4c
Access restrictions:
* Only root user is allowed to open the file.
* APML TSI Register transfer access is read-write.
SBTSI hwmon interface
=====================
The sbtsi_temp auxiliary driver binds to the auxiliary device published
by the core sbtsi driver on the auxiliary bus. The auxiliary device is
named amd-sbtsi.temp-sensor.<id>, where <id> is the device's transfer
address: the client address for I2C, or the assigned-address for I3C.
Note that the auxiliary bus formats <id> in decimal, whereas the
/dev/sbtsi-* misc node formats its address in hex. The two therefore
differ for the same device: an I2C/I3C sensor at address 0x4c appears as the
misc node /dev/sbtsi-4c and the auxiliary device
amd-sbtsi.temp-sensor.76.
It registers a hwmon device, providing a standard Linux hwmon interface
for reading CPU temperature and managing temperature limits.
The hwmon device appears under ``/sys/class/hwmon/`` when both ``sbtsi.ko``
and ``sbtsi_temp.ko`` are loaded.
Verify auxiliary bus device::
ls /sys/bus/auxiliary/devices/
# e.g. amd-sbtsi.temp-sensor.76 for an I2C/I3C sensor at address 0x4c
Example usage::
# Read current temperature
cat /sys/class/hwmon/hwmon<N>/temp1_input
# Set high temperature limit to 70 °C
echo 70000 > /sys/class/hwmon/hwmon<N>/temp1_max
# Verify
cat /sys/class/hwmon/hwmon<N>/temp1_max
Driver IOCTLs
=============
@ -63,6 +123,9 @@ Driver IOCTLs
.. c:macro:: SBRMI_IOCTL_REG_XFER_CMD
.. kernel-doc:: include/uapi/misc/amd-apml.h
:doc: SBRMI_IOCTL_REG_XFER_CMD
.. c:macro:: SBTSI_IOCTL_REG_XFER_CMD
.. kernel-doc:: include/uapi/misc/amd-apml.h
:doc: SBTSI_IOCTL_REG_XFER_CMD
User-space usage
================
@ -85,6 +148,16 @@ Next thing, open the device file, as follows::
exit(1);
}
To open SB-TSI device::
int file;
file = open("/dev/sbtsi-4c", O_RDWR);
if (file < 0) {
/* ERROR HANDLING */
exit(1);
}
The following IOCTLs are defined:
``#define SB_BASE_IOCTL_NR 0xF9``
@ -92,6 +165,7 @@ The following IOCTLs are defined:
``#define SBRMI_IOCTL_CPUID_CMD _IOWR(SB_BASE_IOCTL_NR, 1, struct apml_cpuid_msg)``
``#define SBRMI_IOCTL_MCAMSR_CMD _IOWR(SB_BASE_IOCTL_NR, 2, struct apml_mcamsr_msg)``
``#define SBRMI_IOCTL_REG_XFER_CMD _IOWR(SB_BASE_IOCTL_NR, 3, struct apml_reg_xfer_msg)``
``#define SBTSI_IOCTL_REG_XFER_CMD _IOWR(SB_BASE_IOCTL_NR, 4, struct apml_tsi_xfer_msg)``
User space C-APIs are made available by esmi_oob_library, hosted at