[PATCH v12 0/3] perf: Add Raspberry Pi AXI PMU driver

[Ian Rogers]

Motivation & Background
==============================
Currently, Linux lacks a standard perf-API compatible driver for the
Broadcom AXI performance counter blocks on Raspberry Pi platforms. Prior
out-of-tree vendor solutions relied on custom debugfs nodes and ad-hoc
kthreads, preventing integration with standard Linux perf tooling (`perf stat`,
`perf list`, etc.).

This driver implements standard `struct pmu` hardware uncore callbacks
under `drivers/perf/`, exposing human-readable sysfs event aliases, unit
scaling (`Bytes`), and bus filtering directly to user space.

Key Architectural Improvements & Features
==============================
1. Standard Linux Perf Integration:
   - Exposes uncore AXI interconnect events via `/sys/bus/event_source/devices/rpi_axi_pmu/`.
   - Supports event sampling and hardware counter accumulation (`local64_add`),
     automatically managing 31-bit hardware counter wraparound across high-bandwidth
     interconnect transfers.

2. CPU Hotplug Support (`cpuhp`):
   - Registers dynamic CPU hotplug notifiers (`CPUHP_AP_ONLINE_DYN`).
   - Automatically migrates PMU context (`perf_pmu_migrate_context`) to an online
     CPU core when a designated CPU goes offline, safely guarding memory teardown boundaries.

3. Hybrid Memory-Mapped & Mailbox Work Queue Architecture:
   - System Monitor (MMIO): Performs fast atomic-safe memory reads (~15ns)
     directly mapped over ARM physical memory space (`MON_SYSTEM`).
   - VPU Monitor (Mailbox IPC): For Broadcom BCM2835-BCM2711 platforms (RPi 1-4),
     VideoCore VPU monitor IPC calls are offloaded to process context via a dedicated
     workqueue (`vpu_work`) and serialized under `vpu_mutex`. This avoids atomic
     sleeps or blocking in timer/interrupt context.

4. SoC Generation Support:
   - Patch 1 documents device bindings for Broadcom.
   - Patch 2 adds core driver support for Broadcom BCM2835-BCM2711 (RPi 1-4).
   - Patch 3 expands support for Broadcom BCM2712 (Raspberry Pi 5), adding PCIe RP1
     Southbridge links, HEVC decoder, HVS display engine, and Cortex-A76 DSU L3
     interconnect monitoring dynamically via native MMIO readouts.

Hardware Validation
==============================
The driver has been rigorously validated on real hardware:
- Raspberry Pi 400 (BCM2711): Validated System L2, ARM CPU, and VideoCore
  VPU firmware mailbox IPC performance counters organically spanning
  multi-slice multiplexing boundaries.
- Raspberry Pi 5 (BCM2712): Validated live byte throughput across HVS
  display refresh cycles, Cortex-A76 DSU L3 interconnect memory traffic,
  and PCIe RP1 Southbridge transfers independently configuring `bcm2712_`
  filters.

Changes since v11
==============================
- Decoupled sysfs attribute groups into distinct bcm2835
  (`rpi_axi_pmu_bcm2835_attr_groups`) and BCM2712
  (`rpi_axi_pmu_bcm2712_attr_groups`) arrays dynamically assigned
  during probe based on `.chip`. This officially completely
  eradicates the runtime penalty of scraping string prefixes in
  `.is_visible`.
- Discovered and mitigated a CPU hotplug TOCTOU race vulnerability
  during `rpi_axi_pmu__init` initialization boundaries by introducing
  precise `cpus_read_lock()` atomic block wrapping around the pmu
  registration logic.
- Resolved transient probe dependencies by returning -EPROBE_DEFER
  natively when the mailbox firmware surface has not yet booted,
  preventing silent MMIO fallback.
- Addressed multiple stylistic and naming feedback nits (renamed
  variables using 'pitch' to 'stride', replaced invalid leading
  underscores in function prototypes, and formally introduced the
  MODULE_AUTHOR tag).
- Maintained strict patch separation between BCM2835 Mailbox proxy
  interfaces and BCM2712 native MMIO hardware extensions to streamline
  architectural review parsing.

Ian Rogers (3):
  dt-bindings: perf: Add Broadcom Raspberry Pi AXI PMU definition
  perf: Add Raspberry Pi BCM2835 AXI PMU driver
  perf: Add Raspberry Pi 5 (BCM2712) AXI PMU support

 .../bindings/perf/brcm,bcm2835-axiperf.yaml   |   64 +
 drivers/perf/rpi_axi_pmu.c                    | 2890 +++++++++++++++++
 2 files changed, 2954 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/perf/brcm,bcm2835-axiperf.yaml
 create mode 100644 drivers/perf/rpi_axi_pmu.c

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