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The TMU device can be used as both a clocksource and a clockevent
provider. The driver tries to be smart and power itself on and off, as
well as enabling and disabling its clock when it's not in operation.
This behavior is slightly altered if the TMU is used as an early
platform device in which case the device is left powered on after probe,
but the clock is still enabled and disabled at runtime.
This has worked for a long time, but recent improvements in PREEMPT_RT
and PROVE_LOCKING have highlighted an issue. As the TMU registers itself
as a clockevent provider, clockevents_register_device(), it needs to use
raw spinlocks internally as this is the context of which the clockevent
framework interacts with the TMU driver. However in the context of
holding a raw spinlock the TMU driver can't really manage its power
state or clock with calls to pm_runtime_*() and clk_*() as these calls
end up in other platform drivers using regular spinlocks to control
power and clocks.
This mix of spinlock contexts trips a lockdep warning.
=============================
[ BUG: Invalid wait context ]
6.18.0-arm64-renesas-09926-gee959e7c5e34 #1 Not tainted
-----------------------------
swapper/0/0 is trying to lock:
ffff000008c9e180 (&dev->power.lock){-...}-{3:3}, at: __pm_runtime_resume+0x38/0x88
other info that might help us debug this:
context-{5:5}
1 lock held by swapper/0/0:
ccree e6601000.crypto: ARM CryptoCell 630P Driver: HW version 0xAF400001/0xDCC63000, Driver version 5.0
#0: ffff8000817ec298
ccree e6601000.crypto: ARM ccree device initialized
(tick_broadcast_lock){-...}-{2:2}, at: __tick_broadcast_oneshot_control+0xa4/0x3a8
stack backtrace:
CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.18.0-arm64-renesas-09926-gee959e7c5e34 #1 PREEMPT
Hardware name: Renesas Salvator-X 2nd version board based on r8a77965 (DT)
Call trace:
show_stack+0x14/0x1c (C)
dump_stack_lvl+0x6c/0x90
dump_stack+0x14/0x1c
__lock_acquire+0x904/0x1584
lock_acquire+0x220/0x34c
_raw_spin_lock_irqsave+0x58/0x80
__pm_runtime_resume+0x38/0x88
sh_tmu_clock_event_set_oneshot+0x84/0xd4
clockevents_switch_state+0xfc/0x13c
tick_broadcast_set_event+0x30/0xa4
__tick_broadcast_oneshot_control+0x1e0/0x3a8
tick_broadcast_oneshot_control+0x30/0x40
cpuidle_enter_state+0x40c/0x680
cpuidle_enter+0x30/0x40
do_idle+0x1f4/0x280
cpu_startup_entry+0x34/0x40
kernel_init+0x0/0x130
do_one_initcall+0x0/0x230
__primary_switched+0x88/0x90
For non-PREEMPT_RT builds this is not really an issue, but for
PREEMPT_RT builds where normal spinlocks can sleep this might be an
issue. Be cautious and always leave the power and clock running after
probe.
Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patch.msgid.link/20251202221341.1856773-1-niklas.soderlund+renesas@ragnatech.se
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Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. Quick Start ----------- * Report a bug: See Documentation/admin-guide/reporting-issues.rst * Get the latest kernel: https://kernel.org * Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst * Join the community: https://lore.kernel.org/ Essential Documentation ----------------------- All users should be familiar with: * Building requirements: Documentation/process/changes.rst * Code of Conduct: Documentation/process/code-of-conduct.rst * License: See COPYING Documentation can be built with make htmldocs or viewed online at: https://www.kernel.org/doc/html/latest/ Who Are You? ============ Find your role below: * New Kernel Developer - Getting started with kernel development * Academic Researcher - Studying kernel internals and architecture * Security Expert - Hardening and vulnerability analysis * Backport/Maintenance Engineer - Maintaining stable kernels * System Administrator - Configuring and troubleshooting * Maintainer - Leading subsystems and reviewing patches * Hardware Vendor - Writing drivers for new hardware * Distribution Maintainer - Packaging kernels for distros For Specific Users ================== New Kernel Developer -------------------- Welcome! Start your kernel development journey here: * Getting Started: Documentation/process/development-process.rst * Your First Patch: Documentation/process/submitting-patches.rst * Coding Style: Documentation/process/coding-style.rst * Build System: Documentation/kbuild/index.rst * Development Tools: Documentation/dev-tools/index.rst * Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst * Core APIs: Documentation/core-api/index.rst Academic Researcher ------------------- Explore the kernel's architecture and internals: * Researcher Guidelines: Documentation/process/researcher-guidelines.rst * Memory Management: Documentation/mm/index.rst * Scheduler: Documentation/scheduler/index.rst * Networking Stack: Documentation/networking/index.rst * Filesystems: Documentation/filesystems/index.rst * RCU (Read-Copy Update): Documentation/RCU/index.rst * Locking Primitives: Documentation/locking/index.rst * Power Management: Documentation/power/index.rst Security Expert --------------- Security documentation and hardening guides: * Security Documentation: Documentation/security/index.rst * LSM Development: Documentation/security/lsm-development.rst * Self Protection: Documentation/security/self-protection.rst * Reporting Vulnerabilities: Documentation/process/security-bugs.rst * CVE Procedures: Documentation/process/cve.rst * Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst * Security Features: Documentation/userspace-api/seccomp_filter.rst Backport/Maintenance Engineer ----------------------------- Maintain and stabilize kernel versions: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * Backporting Guide: Documentation/process/backporting.rst * Applying Patches: Documentation/process/applying-patches.rst * Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git for Maintainers: Documentation/maintainer/configure-git.rst System Administrator -------------------- Configure, tune, and troubleshoot Linux systems: * Admin Guide: Documentation/admin-guide/index.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst * Tracing/Debugging: Documentation/trace/index.rst * Performance Security: Documentation/admin-guide/perf-security.rst * Hardware Monitoring: Documentation/hwmon/index.rst Maintainer ---------- Lead kernel subsystems and manage contributions: * Maintainer Handbook: Documentation/maintainer/index.rst * Pull Requests: Documentation/maintainer/pull-requests.rst * Managing Patches: Documentation/maintainer/modifying-patches.rst * Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst * Development Process: Documentation/process/maintainer-handbooks.rst * Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git Configuration: Documentation/maintainer/configure-git.rst Hardware Vendor --------------- Write drivers and support new hardware: * Driver API Guide: Documentation/driver-api/index.rst * Driver Model: Documentation/driver-api/driver-model/driver.rst * Device Drivers: Documentation/driver-api/infrastructure.rst * Bus Types: Documentation/driver-api/driver-model/bus.rst * Device Tree Bindings: Documentation/devicetree/bindings/ * Power Management: Documentation/driver-api/pm/index.rst * DMA API: Documentation/core-api/dma-api.rst Distribution Maintainer ----------------------- Package and distribute the kernel: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * ABI Documentation: Documentation/ABI/README * Kernel Configuration: Documentation/kbuild/kconfig.rst * Module Signing: Documentation/admin-guide/module-signing.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst Communication and Support ========================= * Mailing Lists: https://lore.kernel.org/ * IRC: #kernelnewbies on irc.oftc.net * Bugzilla: https://bugzilla.kernel.org/ * MAINTAINERS file: Lists subsystem maintainers and mailing lists * Email Clients: Documentation/process/email-clients.rst