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

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Message-ID: <CAJZ5v0h1VTozCKweKvma3dQiUCz8KkR88Hue1cL_jDaKiP+BEw@mail.gmail.com>
Date: Fri, 21 Nov 2025 14:10:57 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Val Packett <val@...kett.cool>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Daniel Lezcano <daniel.lezcano@...aro.org>, 
	Christian Loehle <christian.loehle@....com>, 
	Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>, 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 Fri, Nov 21, 2025 at 2:08 AM Val Packett <val@...kett.cool> 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.

So this breaks cpuidle expectations and it doesn't work correctly on
the affected platforms.

> 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.

This generally doesn't work because the new target residency may be
greater than the target residency of the next state.

> Fixes: 76934e495cdc ("cpuidle: Add sanity check for exit latency and target residency")
> Signed-off-by: Val Packett <val@...kett.cool>
> ---
>  drivers/cpuidle/driver.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/cpuidle/driver.c b/drivers/cpuidle/driver.c
> index 1c295a93d582..06aeb59c1017 100644
> --- a/drivers/cpuidle/driver.c
> +++ b/drivers/cpuidle/driver.c
> @@ -199,8 +199,11 @@ static int __cpuidle_driver_init(struct cpuidle_driver *drv)
>                  * exceed its target residency which is assumed in cpuidle in
>                  * multiple places.
>                  */
> -               if (s->exit_latency_ns > s->target_residency_ns)
> -                       return -EINVAL;
> +               if (s->exit_latency_ns > s->target_residency_ns) {
> +                       pr_warn("cpuidle: state %d: exit latency %lld > residency %lld (fixing)\n",
> +                               i, s->exit_latency_ns, s->target_residency_ns);
> +                       s->target_residency_ns = s->exit_latency_ns;

And you also need to update s->target_residency.

Moreover, that needs to be done when all of the target residency and
exit latency values have been computed and full sanitization of all
the states would need to be done (including the ordering checks), but
the kernel has insufficient information to do that (for instance, if
the ordering is not as expected, it is not clear how to fix it up).
Even the above sanitization is unlikely to result in the intended
behavior.

So if returning the error code doesn't work, printing a warning is as
much as can be done, like in the attached patch.

If this works for you, I'll submit it properly later.

> +               }
>         }
>
>         return 0;
> --

View attachment "cpuidle-warn.patch" of type "text/x-patch" (1542 bytes)