linux-kernel - Re: [PATCH v3] soc: samsung: exynos-pmu: Enable CPU Idle for gs101

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Message-ID: <232267bf-d226-43df-bd4f-5977706176a2@kernel.org>
Date: Thu, 3 Jul 2025 12:19:53 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: André Draszik <andre.draszik@...aro.org>,
 Peter Griffin <peter.griffin@...aro.org>,
 Tudor Ambarus <tudor.ambarus@...aro.org>,
 Alim Akhtar <alim.akhtar@...sung.com>
Cc: William Mcvicker <willmcvicker@...gle.com>,
 Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
 linux-arm-kernel@...ts.infradead.org, linux-samsung-soc@...r.kernel.org,
 linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v3] soc: samsung: exynos-pmu: Enable CPU Idle for gs101

On 03/07/2025 12:12, André Draszik wrote:
> Thanks Pete for your patch!
> 
> On Fri, 2025-06-27 at 14:08 +0100, Peter Griffin wrote:
>> Register cpu pm notifiers for gs101 which call the
>> gs101_cpu_pmu_online/offline callbacks which in turn program the ACPM
>> hint. This is required to actually enter the C2 idle state.
>>
>> A couple of corner cases are handled, namely when the system is rebooting
>> or suspending we ignore the request. Additionally the request is ignored if
>> the CPU is in CPU hot plug. Some common code is refactored so that it can
>> be called from both the CPU hot plug callback and CPU PM notifier taking
>> into account that CPU PM notifiers are called with IRQs disabled whereas
>> CPU hotplug callbacks aren't.
>>
>> Note: this patch has a runtime dependency on adding 'local-timer-stop' dt
>> property to the CPU nodes. This informs the time framework to switch to a
>> broadcast timer as the local timer will be shutdown. Without that DT
>> property specified the system hangs in early boot with this patch applied.
>>
>> Signed-off-by: Peter Griffin <peter.griffin@...aro.org>
> 
> With this applied, I see the following during boot:
> 
> [    1.841304][    T0] =============================
> [    1.841422][    T0] [ BUG: Invalid wait context ]
> [    1.841550][    T0] 6.16.0-rc4-next-20250702+ #54 Tainted: G     U          T  
> [    1.841727][    T0] -----------------------------
> [    1.841844][    T0] swapper/0/0 is trying to lock:
> [    1.841965][    T0] ffff000800ee84b8 (&pmu_context->cpupm_lock){....}-{3:3}
> [    1.842001][    T0] , at: gs101_cpu_pm_notify_callback+0x48/0x100
> [    1.842309][    T0] other info that might help us debug this:
> [    1.842613][    T0] context-{5:5}
> [    1.842987][    T0] 1 lock held by swapper/0/0:
> [    1.843442][    T0]  #0: 
> [    1.843859][    T0] ffffafe9d8f1f100
> [    1.844282][    T0]  (
> [    1.844618][    T0] cpu_pm_notifier.lock
> [    1.844980][    T0] ){....}-{2:2}, at: cpu_pm_enter+0x30/0x88
> [    1.845340][    T0] stack backtrace:
> [    1.845855][    T0] CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Tainted: G     U          T   6.16.0-rc4-next-20250702+ #54 PREEMPT 
> [    1.845878][    T0] Tainted: [U]=USER, [T]=RANDSTRUCT
> [    1.845884][    T0] Hardware name: Oriole (DT)
> [    1.845897][    T0] Call trace:
> [    1.845909][    T0]  show_stack+0x24/0x38 (C)
> [    1.845934][    T0]  dump_stack_lvl+0x40/0xc0
> [    1.845949][    T0]  dump_stack+0x18/0x24
> [    1.845956][    T0]  __lock_acquire+0xc68/0xd90
> [    1.845976][    T0]  lock_acquire+0x14c/0x2b8
> [    1.845985][    T0]  _raw_spin_lock+0x54/0x78
> [    1.846011][    T0]  gs101_cpu_pm_notify_callback+0x48/0x100
> [    1.846021][    T0]  notifier_call_chain+0xb0/0x198
> [    1.846046][    T0]  raw_notifier_call_chain_robust+0x50/0xb0
> [    1.846053][    T0]  cpu_pm_enter+0x4c/0x88
> [    1.846063][    T0]  psci_enter_idle_state+0x2c/0x70
> [    1.846078][    T0]  cpuidle_enter_state+0x14c/0x4c0
> [    1.846097][    T0]  cpuidle_enter+0x44/0x68
> [    1.846121][    T0]  do_idle+0x1f0/0x2a8
> [    1.846142][    T0]  cpu_startup_entry+0x40/0x50
> [    1.846152][    T0]  rest_init+0x1c4/0x1d0
> [    1.846161][    T0]  start_kernel+0x358/0x438
> [    1.846181][    T0]  __primary_switched+0x88/0x98

Thanks for the report. Probably such code should be always tested with
lock debugging options enabled, e.g.:
https://github.com/krzk/tools/blob/master/linux/build.sh#L845

Best regards,
Krzysztof