linux-kernel - Re: [PATCH] cpuidle: warn and fixup on sanity check instead of rejecting the driver

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Message-ID: <3abea679-fc83-4157-9d2d-587354b85c68@oss.qualcomm.com>
Date: Fri, 21 Nov 2025 15:50:32 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Val Packett <val@...kett.cool>, "Rafael J. Wysocki" <rafael@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Christian Loehle <christian.loehle@....com>,
        Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>,
        Maulik Shah <maulik.shah@....qualcomm.com>,
        Bjorn Andersson <bjorn.andersson@....qualcomm.com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpuidle: warn and fixup on sanity check instead of
 rejecting the driver

On 11/21/25 2:06 AM, Val Packett wrote:
> On Device Tree platforms, the latency and target residency values come
> directly from device trees, which are numerous and weren't all written
> with cpuidle invariants in mind. For example, qcom/hamoa.dtsi currently
> trips this check: exit latency 680000 > residency 600000.
> 
> Instead of harshly rejecting the entire cpuidle driver with a mysterious
> error message, print a warning and set the target residency value to be
> equal to the exit latency.
> 
> Fixes: 76934e495cdc ("cpuidle: Add sanity check for exit latency and target residency")
> Signed-off-by: Val Packett <val@...kett.cool>
> ---

FWIW this is caused by:

--- hamoa.dtsi
cluster_c4: cpu-sleep-0 {
	compatible = "arm,idle-state";
	idle-state-name = "ret";
	arm,psci-suspend-param = <0x00000004>;
	entry-latency-us = <180>;
	exit-latency-us = <500>;
	min-residency-us = <600>;
};

which notably lacks 'wakeup-latency-us', which triggers this code path:

/*
 * If wakeup-latency-us is missing, default to entry+exit
 * latencies as defined in idle states bindings
 */
idle_state->exit_latency = entry_latency + exit_latency;

which fails this sanity check because 500+180=680 > 600

(which would have been good to note somewhere)


+Maulik can we fix up the numbers somehow?

Konrad