Please see my answer inline.
On 3/6/2018 4:40 AM, Pavel Machek wrote:
Introduction of the Platform Environment Control Interface (PECI) bus
device driver. PECI is a one-wire bus interface that provides a
communication channel between Intel processor and chipset components to
external monitoring or control devices. PECI is designed to support the
following sideband functions:
* Processor and DRAM thermal management
- Processor fan speed control is managed by comparing Digital Thermal
Sensor (DTS) thermal readings acquired via PECI against the
processor-specific fan speed control reference point, or TCONTROL.
Both TCONTROL and DTS thermal readings are accessible via the processor
PECI client. These variables are referenced to a common temperature,
the TCC activation point, and are both defined as negative offsets from
- PECI based access to the processor package configuration space provides
a means for Baseboard Management Controllers (BMC) or other platform
management devices to actively manage the processor and memory power
and thermal features.
* Platform Manageability
- Platform manageability functions including thermal, power, and error
monitoring. Note that platform 'power' management includes monitoring
and control for both the processor and DRAM subsystem to assist with
data center power limiting.
- PECI allows read access to certain error registers in the processor MSR
space and status monitoring registers in the PCI configuration space
within the processor and downstream devices.
- PECI permits writes to certain registers in the processor PCI
* Processor Interface Tuning and Diagnostics
- Processor interface tuning and diagnostics capabilities
(Intel(c) Interconnect BIST). The processors Intel(c) Interconnect
Built In Self Test (Intel(c) IBIST) allows for infield diagnostic
capabilities in the Intel UPI and memory controller interfaces. PECI
provides a port to execute these diagnostics via its PCI Configuration
read and write capabilities.
* Failure Analysis
- Output the state of the processor after a failure for analysis via
PECI uses a single wire for self-clocking and data transfer. The bus
requires no additional control lines. The physical layer is a self-clocked
one-wire bus that begins each bit with a driven, rising edge from an idle
level near zero volts. The duration of the signal driven high depends on
whether the bit value is a logic '0' or logic '1'. PECI also includes
variable data transfer rate established with every message. In this way,
it is highly flexible even though underlying logic is simple.
The interface design was optimized for interfacing to Intel processor and
chipset components in both single processor and multiple processor
environments. The single wire interface provides low board routing
overhead for the multiple load connections in the congested routing area
near the processor and chipset components. Bus speed, error checking, and
low protocol overhead provides adequate link bandwidth and reliability to
transfer critical device operating conditions and configuration
This implementation provides the basic framework to add PECI extensions
to the Linux bus and device models. A hardware specific 'Adapter' driver
can be attached to the PECI bus to provide sideband functions described
above. It is also possible to access all devices on an adapter from
userspace through the /dev interface. A device specific 'Client' driver
also can be attached to the PECI bus so each processor client's features
can be supported by the 'Client' driver through an adapter connection in
the bus. This patch set includes Aspeed 24xx/25xx PECI driver and a generic
PECI hwmon driver as the first implementation for both adapter and client
drivers on the PECI bus framework.
Ok, how does this interact with ACPI/SMM BIOS/Secure mode code? Does
Linux _need_ to control the fan? Or is SMM BIOS capable of doing all
the work itself and Linux has just read-only access for monitoring
This driver is not for local CPUs which this driver is running on.
Instead, this driver will be running on BMC (Baseboard Management
Controller) kernel which is separated from the server machine. In this
implementation, it provides just read-only access for monitoring the
server's CPU and DIMM temperatures remotely through a PECI connection.
The BMC can control fans according to the monitoring data if the BMC has
a fan control interface and feature, but it depends on baseboard
hardware and software designs.
-- (english) http://www.livejournal.com/~pavelmachek
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