[PATCH RESEND RESEND] thermal/of: support thermal zones w/o trips subnode

[PATCH RESEND RESEND] thermal/of: support thermal zones w/o trips subnode

[Icenowy Zheng]

From: Icenowy Zheng <uwu@icenowy.me>

Although the current device tree binding of thermal zones require the
trips subnode, the binding in kernel v5.15 does not require it, and many
device trees shipped with the kernel, for example,
allwinner/sun50i-a64.dtsi and mediatek/mt8183-kukui.dtsi in ARM64, still
comply to the old binding and contain no trips subnode.

Allow the code to successfully register thermal zones w/o trips subnode
for DT binding compatibility now.

Furtherly, the inconsistency between DTs and bindings should be resolved
by either adding empty trips subnode or dropping the trips subnode
requirement.

Fixes: d0c75fa2c17f ("thermal/of: Initialize trip points separately")
Signed-off-by: Icenowy Zheng <uwu@icenowy.me>
---

Unfortunately the code gets dropped by mailing lists again and again...

Sorry for the disturbance.

 drivers/thermal/thermal_of.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/thermal/thermal_of.c b/drivers/thermal/thermal_of.c
index 6fb14e521197..2c76df847e84 100644
--- a/drivers/thermal/thermal_of.c
+++ b/drivers/thermal/thermal_of.c
@@ -127,15 +127,17 @@ static struct thermal_trip *thermal_of_trips_init(struct device_node *np, int *n
 
 	trips = of_get_child_by_name(np, "trips");
 	if (!trips) {
-		pr_err("Failed to find 'trips' node\n");
-		return ERR_PTR(-EINVAL);
+		pr_debug("Failed to find 'trips' node\n");
+		*ntrips = 0;
+		return NULL;
 	}
 
 	count = of_get_child_count(trips);
 	if (!count) {
-		pr_err("No trip point defined\n");
-		ret = -EINVAL;
-		goto out_of_node_put;
+		pr_debug("No trip point defined\n");
+		of_node_put(trips);
+		*ntrips = 0;
+		return NULL;
 	}
 
 	tt = kzalloc(sizeof(*tt) * count, GFP_KERNEL);
@@ -519,7 +521,10 @@ static struct thermal_zone_device *thermal_of_zone_register(struct device_node *
 	of_ops->bind = thermal_of_bind;
 	of_ops->unbind = thermal_of_unbind;
 
-	mask = GENMASK_ULL((ntrips) - 1, 0);
+	if (ntrips)
+		mask = GENMASK_ULL((ntrips) - 1, 0);
+	else
+		mask = 0;
 
 	tz = thermal_zone_device_register_with_trips(np->name, trips, ntrips,
 						     mask, data, of_ops, tzp,
-- 
2.39.1


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Re: [PATCH RESEND RESEND] thermal/of: support thermal zones w/o trips subnode

[Mark Brown]

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On Sat, Jul 22, 2023 at 08:25:34PM +0800, Icenowy Zheng wrote:
> From: Icenowy Zheng <uwu@icenowy.me>
> 
> Although the current device tree binding of thermal zones require the
> trips subnode, the binding in kernel v5.15 does not require it, and many
> device trees shipped with the kernel, for example,
> allwinner/sun50i-a64.dtsi and mediatek/mt8183-kukui.dtsi in ARM64, still
> comply to the old binding and contain no trips subnode.
> 
> Allow the code to successfully register thermal zones w/o trips subnode
> for DT binding compatibility now.
> 
> Furtherly, the inconsistency between DTs and bindings should be resolved
> by either adding empty trips subnode or dropping the trips subnode
> requirement.

This makes sense to me - it allows people to see the reported
temperature even if there's no trips defined which seems more
helpful than refusing to register.

Reviewed-by: Mark Brown <broonie@kernel.org>

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Re: [PATCH RESEND RESEND] thermal/of: support thermal zones w/o trips subnode

[Daniel Lezcano]

Hi Mark,

On 22/07/2023 22:11, Mark Brown wrote:
> On Sat, Jul 22, 2023 at 08:25:34PM +0800, Icenowy Zheng wrote:
>> From: Icenowy Zheng <uwu@icenowy.me>
>>
>> Although the current device tree binding of thermal zones require the
>> trips subnode, the binding in kernel v5.15 does not require it, and many
>> device trees shipped with the kernel, for example,
>> allwinner/sun50i-a64.dtsi and mediatek/mt8183-kukui.dtsi in ARM64, still
>> comply to the old binding and contain no trips subnode.
>>
>> Allow the code to successfully register thermal zones w/o trips subnode
>> for DT binding compatibility now.
>>
>> Furtherly, the inconsistency between DTs and bindings should be resolved
>> by either adding empty trips subnode or dropping the trips subnode
>> requirement.
> 
> This makes sense to me - it allows people to see the reported
> temperature even if there's no trips defined which seems more
> helpful than refusing to register.

The binding describes the trip points as required and that since the 
beginning.

What changed is now the code reflects the required property while before 
it was permissive, that was an oversight.

Just a reminder about the thermal framework goals:

   1. It protects the silicon (thus critical and hot trip points)

   2. It mitigates the temperature (thus cooling device bound to trip 
points)

   3. It notifies the userspace when a trip point is crossed

So if the thermal zone is described but without any of this goal above, 
it is pointless.

If the goal is to report the temperature only, then hwmon should be used 
instead.

If the goal is to mitigate by userspace, then the trip point *must* be 
used to prevent the userspace polling the temperature. With the trip 
point the sensor will be set to fire an interrupt at the given trip 
temperature.

IOW, trip points are not optional



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Re: [PATCH RESEND RESEND] thermal/of: support thermal zones w/o trips subnode

[Icenowy Zheng]

在 2023-07-24星期一的 12:25 +0800，Chen-Yu Tsai写道：
> On Sun, Jul 23, 2023 at 12:12:49PM +0200, Daniel Lezcano wrote:
> > 
> > Hi Mark,
> > 
> > On 22/07/2023 22:11, Mark Brown wrote:
> > > On Sat, Jul 22, 2023 at 08:25:34PM +0800, Icenowy Zheng wrote:
> > > > From: Icenowy Zheng <uwu@icenowy.me>
> > > > 
> > > > Although the current device tree binding of thermal zones
> > > > require the
> > > > trips subnode, the binding in kernel v5.15 does not require it,
> > > > and many
> > > > device trees shipped with the kernel, for example,
> > > > allwinner/sun50i-a64.dtsi and mediatek/mt8183-kukui.dtsi in
> > > > ARM64, still
> > > > comply to the old binding and contain no trips subnode.
> > > > 
> > > > Allow the code to successfully register thermal zones w/o trips
> > > > subnode
> > > > for DT binding compatibility now.
> > > > 
> > > > Furtherly, the inconsistency between DTs and bindings should be
> > > > resolved
> > > > by either adding empty trips subnode or dropping the trips
> > > > subnode
> > > > requirement.
> > > 
> > > This makes sense to me - it allows people to see the reported
> > > temperature even if there's no trips defined which seems more
> > > helpful than refusing to register.
> > 
> > The binding describes the trip points as required and that since
> > the
> > beginning.
> 
> Not really. It was made optional in the v5.15 kernel release by
> commit
> 
>     22fc857538c3 dt-bindings: thermal: Make trips node optional

I agree, this is why I send this patch (and why I say 'for DT binding
compatibility now' in the commit message). Further discussion could be
performed, but this patch should be applied regardless of the result of
further discussion.

DT binding compatibility is the unbreakable law.

> 
> > What changed is now the code reflects the required property while
> > before it
> > was permissive, that was an oversight.
> > 
> > Just a reminder about the thermal framework goals:
> > 
> >   1. It protects the silicon (thus critical and hot trip points)
> > 
> >   2. It mitigates the temperature (thus cooling device bound to
> > trip points)
> > 
> >   3. It notifies the userspace when a trip point is crossed
> > 
> > So if the thermal zone is described but without any of this goal
> > above, it
> > is pointless.
> > 
> > If the goal is to report the temperature only, then hwmon should be
> > used
> > instead.
> 
> What about thermal sensors with multiple channels? Some of the
> channels
> are indeed tied to important hardware blocks like the CPU cores and
> should be tied into the thermal tripping. However other channels
> might
> only be used for temperature read-out and have no such requirement.
> 
> Should we be mixing thermal and hwmon APIs in the driver?

Well you have no right to decide which sensor should be used for
throttling and which not. So the only way to make the semantic correct
is just rip every sensor driver out of thermal API to hwmon API, and
let thermal framework to use hwmon's.

> 
> > If the goal is to mitigate by userspace, then the trip point *must*
> > be used
> > to prevent the userspace polling the temperature. With the trip
> > point the
> > sensor will be set to fire an interrupt at the given trip
> > temperature.
> > 
> > IOW, trip points are not optional
> 
> for measurement points that are used for thermal throttling /
> mitigation.
> 
> ChenYu
> 


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Re: [PATCH RESEND RESEND] thermal/of: support thermal zones w/o trips subnode

[Daniel Lezcano]

On 22/07/2023 14:25, Icenowy Zheng wrote:
> From: Icenowy Zheng <uwu@icenowy.me>
> 
> Although the current device tree binding of thermal zones require the
> trips subnode, the binding in kernel v5.15 does not require it, and many
> device trees shipped with the kernel, for example,
> allwinner/sun50i-a64.dtsi and mediatek/mt8183-kukui.dtsi in ARM64, still
> comply to the old binding and contain no trips subnode.
> 
> Allow the code to successfully register thermal zones w/o trips subnode
> for DT binding compatibility now.
> 
> Furtherly, the inconsistency between DTs and bindings should be resolved
> by either adding empty trips subnode or dropping the trips subnode
> requirement.
> 
> Fixes: d0c75fa2c17f ("thermal/of: Initialize trip points separately")
> Signed-off-by: Icenowy Zheng <uwu@icenowy.me>
> ---
> 
> Unfortunately the code gets dropped by mailing lists again and again...
> 
> Sorry for the disturbance.
> 
>   drivers/thermal/thermal_of.c | 17 +++++++++++------
>   1 file changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/thermal/thermal_of.c b/drivers/thermal/thermal_of.c
> index 6fb14e521197..2c76df847e84 100644
> --- a/drivers/thermal/thermal_of.c
> +++ b/drivers/thermal/thermal_of.c
> @@ -127,15 +127,17 @@ static struct thermal_trip *thermal_of_trips_init(struct device_node *np, int *n
>   
>   	trips = of_get_child_by_name(np, "trips");
>   	if (!trips) {
> -		pr_err("Failed to find 'trips' node\n");
> -		return ERR_PTR(-EINVAL);
> +		pr_debug("Failed to find 'trips' node\n");
> +		*ntrips = 0;

set ntrips at the beginning of the function.

> +		return NULL;

return ERR_PTR(-ENXIO);

>   	}
>   
>   	count = of_get_child_count(trips);
>   	if (!count) {
> -		pr_err("No trip point defined\n");
> -		ret = -EINVAL;
> -		goto out_of_node_put;
> +		pr_debug("No trip point defined\n");
> +		of_node_put(trips);
> +		*ntrips = 0;
> +		return NULL;

Why not keep goto out_of_node_put ?

>   	}
>   
>   	tt = kzalloc(sizeof(*tt) * count, GFP_KERNEL);
> @@ -519,7 +521,10 @@ static struct thermal_zone_device *thermal_of_zone_register(struct device_node *


The function should check the return value of thermal_of_trips_init()

If this one returns -ENXIO, it should pr_warn().

>   	of_ops->bind = thermal_of_bind;
>   	of_ops->unbind = thermal_of_unbind;
>   
> -	mask = GENMASK_ULL((ntrips) - 1, 0);
> +	if (ntrips)
> +		mask = GENMASK_ULL((ntrips) - 1, 0);
> +	else
> +		mask = 0;

	mask = ntrips ? GENMASK_ULL((ntrips) - 1, 0) : 0;

>   	tz = thermal_zone_device_register_with_trips(np->name, trips, ntrips,
>   						     mask, data, of_ops, tzp,

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