linux-kernel - [RFC/PATCH 0/2] clocksource/drivers/sh

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Message-ID: <20250828214403.1765311-1-niklas.soderlund+renesas@ragnatech.se>
Date: Thu, 28 Aug 2025 23:44:01 +0200
From: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>
To: Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org,
	linux-renesas-soc@...r.kernel.org
Cc: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>
Subject: [RFC/PATCH 0/2] clocksource/drivers/sh_cmt: Improve clock event design

Hello,

This RFC/PATCH tries to address an issue with the Renesas CMT driver 
design. The driver do PM and clock handling in struct clock_event_device 
callbacks. This leads to LOCKDEP warnings and I think hints at a larger 
issue.

    =============================
    [ BUG: Invalid wait context ]
    6.17.0-rc3-arm64-renesas-03071-gb3c4f4122b28-dirty #21 Not tainted
    -----------------------------
    swapper/1/0 is trying to lock:
    ffff00000898d180 (&dev->power.lock){-...}-{3:3}, at: __pm_runtime_resume+0x38/0x88
    ccree e6601000.crypto: ARM CryptoCell 630P Driver: HW version 0xAF400001/0xDCC63000, Driver version 5.0
    other info that might help us debug this:
    ccree e6601000.crypto: ARM ccree device initialized
    context-{5:5}
    2 locks held by swapper/1/0:
     #0: ffff80008173c298 (tick_broadcast_lock){-...}-{2:2}, at: __tick_broadcast_oneshot_control+0xa4/0x3a8
     #1: ffff0000089a5858 (&ch->lock){....}-{2:2}
    usbcore: registered new interface driver usbhid
    , at: sh_cmt_start+0x30/0x364
    stack backtrace:
    CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Not tainted 6.17.0-rc3-arm64-renesas-03071-gb3c4f4122b28-dirty #21 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_cmt_start+0x54/0x364
     sh_cmt_clock_event_set_oneshot+0x64/0xb8
     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+0x1f4/0x26c
     cpu_startup_entry+0x34/0x40
     secondary_start_kernel+0x11c/0x13c
     __secondary_switched+0x74/0x78

This series tries to address this by instead doing PM and clock 
management at probe time, and leaving them on for the CMT channels that 
are used as clock events. The CMT design is a bit messy as channels can 
be used both as clock sources and events. And the design to do the 
housekeeping for clock sources seems to be valid and is kept.

This is posted as an RFC as there is one other driver in-tree that 
suffers form similar issues. I intend to try and refactor that away too, 
but would like to try and get some feedback first.

The work is tested on R-Car M3N.

Niklas Söderlund (2):
  clocksource/drivers/sh_cmt: Split start/stop of clock source and
    events
  clocksource/drivers/sh_cmt: Do not power down channels used for events

 drivers/clocksource/sh_cmt.c | 85 +++++++++++++++++++++++-------------
 1 file changed, 54 insertions(+), 31 deletions(-)

-- 
2.51.0