linux-kernel - Re: [PATCH v1 1/6] thermal: trip: Simplify computing trip indices

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Date:   Fri, 20 Oct 2023 17:58:51 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Zhang Rui <rui.zhang@...el.com>,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v1 1/6] thermal: trip: Simplify computing trip indices



On 10/6/23 18:40, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> A trip index can be computed right away as a difference between the
> value of a trip pointer pointing to the given trip object and the
> start of the trips[] table in the thermal zone containing the trip, so
> change thermal_zone_trip_id() accordingly.
> 
> No intentional functional impact (except for some speedup).
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>   drivers/thermal/thermal_trip.c |   13 +++++--------
>   1 file changed, 5 insertions(+), 8 deletions(-)
> 
> Index: linux-pm/drivers/thermal/thermal_trip.c
> ===================================================================
> --- linux-pm.orig/drivers/thermal/thermal_trip.c
> +++ linux-pm/drivers/thermal/thermal_trip.c
> @@ -175,14 +175,11 @@ int thermal_zone_set_trip(struct thermal
>   int thermal_zone_trip_id(struct thermal_zone_device *tz,
>   			 const struct thermal_trip *trip)
>   {
> -	int i;
> -
>   	lockdep_assert_held(&tz->lock);
>   
> -	for (i = 0; i < tz->num_trips; i++) {
> -		if (&tz->trips[i] == trip)
> -			return i;
> -	}
> -
> -	return -ENODATA;
> +	/*
> +	 * Assume the trip to be located within the bounds of the thermal
> +	 * zone's trips[] table.
> +	 */
> +	return trip - tz->trips;
>   }
> 
> 
> 

I agree wit hthe comment, we should be safe here, since we control that
array.

I could be a bit picky about this 'int' return in that function on
64bit kernels, were we have also ptrdiff_t set to long IIRC. But this
particular usage should be handled properly in all our cases, so:

Reviewed-by: Lukasz Luba <lukasz.luba@....com>
Tested-by: Lukasz Luba <lukasz.luba@....com>