From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f70.google.com (mail-pj1-f70.google.com [209.85.216.70]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 85C5642AFB1 for ; Wed, 12 Aug 2026 23:08:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.70 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786576087; cv=none; b=PJRDofhjBPqDEXljV/wFj1M4fMn+YHvRqQvzYLzUHflPOjHytN2h4ZkthH4JcwGY39jcq2/xhjVsHGf5g4Xppk/I93aljKtLeMxNFKtWT3B4I9LGpsoytwAXE29edHcfCHSEL27GHn/I18VzvyEkmyISh7FQ+amXQwAsFh3+zDc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786576087; c=relaxed/simple; bh=Cbz9apUK6WeVQ7Ai32nThEUSX7Znc3/LmVgOmqTkvFE=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=QWPEThkedulBVC1sPwjHLPdKEyEL23q2y4SwDlLxdb9/wOVKnR50HChIEbvQw/9LF26dzKsL25PpDTVTbtYXCD9hOuBJarEWD5V39FFzYiSWL79ZiBJ1MnF/cEJaXtwrjTdqC8zZG+QvuPNdbBc4klc2/kTzp0ozNgW/eUwgqdU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--irogers.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=kl1ylwOO; arc=none smtp.client-ip=209.85.216.70 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--irogers.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="kl1ylwOO" Received: by mail-pj1-f70.google.com with SMTP id 98e67ed59e1d1-38e1118e4abso257559a91.0 for ; Wed, 12 Aug 2026 16:08:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1786576086; x=1787180886; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:from:to:cc:subject:date:message-id:reply-to :content-type; bh=tlmwDWahDCpqVEzTLP2aJg+dpiOPXi64VDUj/j5mYu8=; b=kl1ylwOOL0EJ58VT0tEF9o+2+VgS5F7sE2Ur+GScVeL9EHf1VswZGP0UvwaG4RbjcC RZ0iao2TbsN7sH1geffCufLfmKXfdJGxAIAdheX8dm9SYhJjLP0KrcNc/BR16Gudh9h9 HR6qf04BYLah5L8ECPQuwfOQkEpmuHoSnWP9nG614BR6nLfPzYuuklP40MxMzfCijHIZ axlPE24Hz111uDnI+GfsH/LoJn9tdF05z3JEAIUUKWHx48rUeGIibtezgHfoVXNF7bNz r2bqv2zVNhR8upyqqVzhcrUOPfy3rRsaaa3U2JUg2KLGx8sbu9C3uSr13GbbiWL5ccpt puig== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1786576086; x=1787180886; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=tlmwDWahDCpqVEzTLP2aJg+dpiOPXi64VDUj/j5mYu8=; b=fMS6/awHBRO4w/o3JDeWxzo6J7bas0z0n6cvzwl5Kvf4DBqBbQwZVca2XY/KgKVS0+ 3ACsfUAWvD/HpHQvmanwMPfR04iEh3FlllHRVLbxZE5zOwTlholMUO4tSKr2vAzL7Ajr yxZXP/UsYaFOyduel4Uag6DM3gS0DNhiln/kaO9vKSoAIKwgBMpRVQekBRHc8SmrPfZg 8wkpRyCoDtF+yI97tWE8qibSMPGvnfJ5ewp0mGwvs+WkCvP9tSarkhf5l/JItqk4MJk6 yccYCLR2GvkENmqkNGHKD/6oYZ3lAB+Kh9jadXTIuozupNAxO//TLGelY6BABhqhHf3g mvRA== X-Forwarded-Encrypted: i=1; AHgh+RpoIP4Zq6eDPZejFpo7a8rRt8qBC1ydFoICfl4nVbk3/MgQdg48sX50RHPz3oSaVrDpUvuhY+qY+nJghGz3YvTC@vger.kernel.org X-Gm-Message-State: AOJu0Yzn6a/1g9BaRXdiDJLdjQ0TOuyjb8gW4qqK1ob7fvoJThbJ6GN9 VY+mt8+dP/VqH6TPlK9sYWvftKQPP8+seMwbzHHI1VOkCnIuMDR0cw9vFIJhGsQwNvIlU7gI9mx 6KWetqFoLEg== X-Received: from dlbvg26.prod.google.com ([2002:a05:7022:7f1a:b0:13c:dac9:90ed]) (user=irogers job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:2644:b0:38f:1dc:672f with SMTP id 98e67ed59e1d1-3931e29843cmr1958999a91.18.1786576085578; Wed, 12 Aug 2026 16:08:05 -0700 (PDT) Date: Wed, 12 Aug 2026 16:07:58 -0700 In-Reply-To: <20260812230145.2644281-1-irogers@google.com> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260812230145.2644281-1-irogers@google.com> X-Mailer: git-send-email 2.55.0.691.gc56d675ccc-goog Message-ID: <20260812230800.2646749-1-irogers@google.com> Subject: [PATCH v5 0/2] perf: Add Raspberry Pi AXI PMU driver From: Ian Rogers To: irogers@google.com, linux-perf-users@vger.kernel.org, linux-rpi-kernel@lists.infradead.org Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, mark.rutland@arm.com, u.kleine-koenig@baylibre.com, will@kernel.org Content-Type: text/plain; charset="UTF-8" This patch series adds an uncore Performance Monitoring Unit (PMU) driver for Broadcom AXI system and VideoCore VPU performance monitors found on Raspberry Pi SoCs (BCM2835 through BCM2712 / Raspberry Pi 1 through 5). 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, avoiding stale uncore state. 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. PREEMPT_RT & Safety Hardening: - Uses HRTIMER_MODE_REL_SOFT for timer callbacks to execute in softirq context, ensuring spinlock acquisitions are 100% PREEMPT_RT safe. - Sets suppress_bind_attrs = true to prevent unsafe manual sysfs unbinding while active perf events exist. 5. SoC Generation Support: - Patch 1 adds core driver support for Broadcom BCM2835-BCM2711 (RPi 1-4). - Patch 2 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. Hardware Validation ------------------- The driver has been validated on real hardware across multiple SoC generations: - Raspberry Pi 400 (BCM2711): Validated System L2, ARM CPU, and VideoCore VPU firmware mailbox IPC performance counters. - 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. Changes in v5 ------------- - Teardown UAF/Orphaning Fix: Reversed module exit logic, calling cpuhp_state_remove_instance() *before* perf_pmu_unregister() to prevent accessing an unregistered PMU in the offline CPU handler during device removal, and to prevent event orphaning races during hotplug. - VPU Hardware Watcher Leak Fix: In rpi_axi_pmu_del(), hardware disablement operations for VPU bus watchers are now properly deferred to the vpu_work workqueue to avoid silently leaking running hardware counters when the VPU monitor is no longer in use. - Grouped Event Start Bug Fix: Deprecated reliance on num_monitored == 1 to initialize the global bus watcher. Instead, use a dedicated monitor_running flag correctly to start the global monitor when the first bus watcher gets enabled, mitigating bugs when adding grouped PMU events. - IPC Phantom Spikes Zero Fallback Fix: Modified rpi_axi_pmu_read_counter() to return U32_MAX on IPC or MMIO hardware read failures, gracefully ignoring the delta calculation returning. This fixes unsigned 31-bit huge spikes where delta (0 - old_count) & 0x7FFFFFFF occurred. - Code Comments: Added doc block comments inside rpi_axi_pmu_read(), rpi_axi_pmu_vpu_work_handler(), and everywhere U32_MAX returns occur to document the explicit justification for why U32_MAX indicates failure (valid counters are 31-bit) and why the driver drops the sample to avoid artificial spikes. - VPU Data Race Lockdep Fix: Rewrote locking hierarchy inside vpu_work_handler(). PMU spinlock is now correctly held across rpi_axi_pmu_enable_bus_watcher() unconditionally since the function touches active monitor registers directly via MMIO, dropping it purely for mailbox IPC reads. - Hrtimer Add/Del Forward Concurrency Warning Fix: rpi_axi_pmu_timer_handler() now executes hrtimer_forward_now() *before* releasing the PMU spinlock, fully mitigating timer enqueue races resulting from a simultaneous parallel pmu->add()/pmu->del(). - VPU Start Asynchronous Latency: Added explicit schedule_work(&pmu->vpu_work) call inside rpi_axi_pmu_start() when starting VPU-tracked events so they begin immediately instead of waiting for a 2-second timer interrupt period for short workloads. - Event Stop Read-Modify-Write Spinlock Protection: Moved event->hw.state modifications inside rpi_axi_pmu_stop() under the local CPU PMU irqsave spinlock to safeguard atomic bitwise flags against the timer handler or workqueue updates. - BCM2712 Pre-probe Initializer UAF race: Shifted perf_pmu_register() to the very end of rpi_axi_pmu__init() to ensure all hardware structures and CPU HP bindings securely exist prior to exposing the PMU to userspace tools preventing devres unregistration memory faults. - BCM2712 ARM CPU L2 Event Correction: Corrected the bus index for the Cortex-A76 Cores PMU event aliases to bus=14 (BCM2712_SB__CPU_L2) to match architectural routing specifications on the RPi 5. - BCM2712 JPEG Bus Monitor Visibility: Stopped improperly hiding the legacy JPEG bus aliases in the is_visible() callback on BCM2712 chips. - BCM2712 Custom Event Replacements: Created specific BCM2712 equivalents for peripheral_rtrans/wtrans and cpu_uc_rtrans/wtrans since raw bus mappings shifted structurally on VideoCore VII. Ian Rogers (2): perf: Add Raspberry Pi BCM2835 AXI PMU driver perf: Add Raspberry Pi 5 (BCM2712) AXI PMU support drivers/perf/Kconfig | 10 + drivers/perf/Makefile | 1 + drivers/perf/rpi_axi_pmu.c | 2124 ++++++++++++++++++++++++++++++++++++ 3 files changed, 2135 insertions(+) create mode 100644 drivers/perf/rpi_axi_pmu.c -- 2.55.0.691.gc56d675ccc-goog