linux-kernel - Re: [PATCH v2 8/9] thermal: of: Set THERMAL_TRIP_FLAG_RW

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Date: Thu, 22 Feb 2024 14:48:39 +0100
From: Daniel Lezcano <daniel.lezcano@...aro.org>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>,
 Linux PM <linux-pm@...r.kernel.org>
Cc: Lukasz Luba <lukasz.luba@....com>, LKML <linux-kernel@...r.kernel.org>,
 Stanislaw Gruszka <stanislaw.gruszka@...ux.intel.com>,
 Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
 Zhang Rui <rui.zhang@...el.com>, netdev@...r.kernel.org,
 Ido Schimmel <idosch@...dia.com>, Petr Machata <petrm@...dia.com>,
 Miri Korenblit <miriam.rachel.korenblit@...el.com>,
 linux-wireless@...r.kernel.org, Shawn Guo <shawnguo@...nel.org>,
 Sascha Hauer <s.hauer@...gutronix.de>,
 Pengutronix Kernel Team <kernel@...gutronix.de>,
 Manaf Meethalavalappu Pallikunhi <quic_manafm@...cinc.com>
Subject: Re: [PATCH v2 8/9] thermal: of: Set THERMAL_TRIP_FLAG_RW_TEMP
 directly

On 12/02/2024 19:40, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> It is now possible to flag trip points with THERMAL_TRIP_FLAG_RW_TEMP
> to allow their temperature to be set from user space via sysfs instead
> of using a nonzero writable trips mask during thermal zone registration,
> so make the OF thermal code do that.
> 
> No intentional functional impact.
> 
> Note that this change is requisite for dropping the mask argument from
> thermal_zone_device_register_with_trips() going forward.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
> 
> v1 -> v2: Rename trip flag (Stanislaw).
> 
> ---
>   drivers/thermal/thermal_of.c |    8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> Index: linux-pm/drivers/thermal/thermal_of.c
> ===================================================================
> --- linux-pm.orig/drivers/thermal/thermal_of.c
> +++ linux-pm/drivers/thermal/thermal_of.c
> @@ -117,6 +117,8 @@ static int thermal_of_populate_trip(stru
>   		return ret;
>   	}
>   
> +	trip->flags = THERMAL_TRIP_FLAG_RW_TEMP;
> +
>   	return 0;
>   }

Even if you are not at the origin of this default behavior. I'm 
wondering if we should be more protective against changes from userspace 
when the firmware is telling us to protect the silicon at a specific 
temperature.

What do you think if we set the THERMAL_TRIP_FLAG_RW_TEMP only if the 
trip point is not bound to a cooling device?

So trip points without associated cooling device can be writable but 
others can be considered as managed by the kernel and no modifiable.

(This comment does not put in question this patch BTW)

> @@ -477,7 +479,7 @@ static struct thermal_zone_device *therm
>   	struct device_node *np;
>   	const char *action;
>   	int delay, pdelay;
> -	int ntrips, mask;
> +	int ntrips;
>   	int ret;
>   
>   	of_ops = kmemdup(ops, sizeof(*ops), GFP_KERNEL);
> @@ -510,15 +512,13 @@ static struct thermal_zone_device *therm
>   	of_ops->bind = thermal_of_bind;
>   	of_ops->unbind = thermal_of_unbind;
>   
> -	mask = GENMASK_ULL((ntrips) - 1, 0);
> -
>   	ret = of_property_read_string(np, "critical-action", &action);
>   	if (!ret)
>   		if (!of_ops->critical && !strcasecmp(action, "reboot"))
>   			of_ops->critical = thermal_zone_device_critical_reboot;
>   
>   	tz = thermal_zone_device_register_with_trips(np->name, trips, ntrips,
> -						     mask, data, of_ops, &tzp,
> +						     0, data, of_ops, &tzp,
>   						     pdelay, delay);
>   	if (IS_ERR(tz)) {
>   		ret = PTR_ERR(tz);
> 
> 
> 

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