Add Dynamic Voltage and Frequency Scaling Driver Class

.gitignore

@@ -20,6 +20,7 @@ ci_logs/
 zig-out/
 .zig-cache/
 venv/
+target/
 __pycache__
 .*.sw*
 *.dtb

.reuse/dep5

@@ -35,6 +35,7 @@ Files:
     drivers/timer/cdns/config.json
     drivers/timer/bcm2835/config.json
     drivers/timer/apb_timer/config.json
+    drivers/dvfs/Cargo.lock
 Copyright: UNSW
 License: BSD-2-Clause
 
@@ -52,3 +53,7 @@ License: ISC
 Files: network/ipstacks/lwip/*
 Copyright: Copyright (c) 2001-2004 Swedish Institute of Computer Science
 License: LicenseRef-BSD-LWIP
+
+Files: support/targets/aarch64-sel4-microkit-minimal.json
+Copyright: Copyright 2023, Colias Group, LLC
+License: BSD-2-Clause

docs/design/design.tex

@@ -2542,9 +2542,92 @@ \subsection{Status}
 
 This device-class specification is \textbf{subject to change}.
 
+\section{Dynamic Voltage and Frequency Scaling}\label{s:DVFS}
+Dynamic Voltage and Frequency Scaling(DVFS) is a power management technology
+to adjust the frequency and the voltage applied on the processing units in runtime
+depending on the actual needs.
+
+\subsection{Principle of the operation}
+The power consumption of CMOS(Complementary Metal-Oxide-Semiconductor) circuits can
+be defined by the following formula:
+
+\begin{equation}
+    P_{total} = P_{dynamic} + P_{static}
+\end{equation}
+
+Where dynamic power can be roughly defined as:
+
+\begin{equation}
+    P_{dynamic} \approx C \cdot V^2 \cdot f
+\end{equation}
+
+\begin{itemize}
+    \item \textbf{C}: Capacitance (fixed by hardware design).
+    \item \textbf{V}: Supply Voltage.
+    \item \textbf{f}: Clock Frequency.
+\end{itemize}
+
+The power scales linearly with the frequency and quadratically with voltage. Lowering
+the frequency, which usually allows a lower supply voltage, can dramatically lower
+the power consumption as well as the generated heat.
+
+\subsection{Implementing DVFS on different platforms}
+There are generally two ways to implement DVFS, and which one to use is heavily depended
+on the hardware platform.
+
+\paragraph{Direct interact with the clock/regulator:} The DVFS driver directly interacts
+with the clock and the regulator that control the frequency and the voltage the processing
+units are operating on. This approach is used on most of the ARM or RISC-V platforms.
+
+\paragraph{Firmware Abstraction:} For some very new ARM platforms, System Control and
+Management Interface (SCMI) is supported, providing a unified framework to manage the
+the power state of the processing units. For x86 platforms, ACPI and HWP are the common
+framework to provide platform agnostic power management interfaces.
+
+\subsection{Data Structures and Interface Specification}
+The interface contains static configuration tables to describe the hardware. These are
+exposed to the client at compile time.
+
+\paragraph{Operating Performance Point}
+Describes a valid discrete state the processing unit can operate on.
+\begin{lstlisting}
+typedef struct {
+    uint64_t freq_hz;     // Target Frequency in Hertz
+    uint64_t voltage_uv;  // Target Voltage in Microvolts
+    uint64_t latency_ns;  // Transition latency in Nanoseconds
+} OppEntry;
+\end{lstlisting}
+
+\paragraph{Core Configuration (CoreInfo)}
+Describes the topology of the processor. The configuration describes
+the number of the processing units, the clock source they are operating under
+(one clock source may provide clock for multiple processing units, which means
+changing the frequency for one unit would change the frequency of all the units
+which has the same clock source), and the Operating Performance Point table.
+
+\begin{lstlisting}
+typedef struct {
+    uint64_t core_ident;         // Logical Core ID
+    uint64_t clock_source_ident; // ID of the clock source
+    const OppEntry *opptable;    // Pointer to valid OPPs for this core
+    size_t opptable_len;         // Number of OPPs
+} CoreInfo;
+\end{lstlisting}
+
+The interface for DVFS uses \gls{ppc}, and has the following
+procedures that can be called:
+\begin{description}
+  \item[\texttt{get\_freq(core\_identifier)}]
+  Retrieves the current actual frequency of a specific processing unit.
+  \item[\texttt{set\_freq(core\_identifier, frequency)}]
+  Sets the designated processing unit to a specific target frequency. The frequency
+  must be a valid value from the opp table for that specific core or the request
+  will be rejected.
+\end{description}
+
 \section{Sensors, PWM, GPIO, etc}\label{s:sensors}
 
-These device classes are all very similar, and tend tend to be low
+These device classes are all very similar, and tend to be low
 bandwidth --- transferring one bit to a few bytes at a time.  They
 fall into the ``simple device'' category introduced in
 \autoref{s:dr-overview}; rather than

drivers/dvfs/.cargo/config.toml

@@ -0,0 +1,14 @@
+# Copyright 2025, UNSW
+# SPDX-License-Identifier: BSD-2-Clause
+
+[build]
+target = "../../support/targets/aarch64-sel4-microkit-minimal.json"
+
+[unstable]
+build-std = ["core", "compiler_builtins", "alloc"]
+build-std-features = ["compiler-builtins-mem"]
+
+[net]
+git-fetch-with-cli = true
+
+[target."aarch64-sel4-microkit-minimal"]