linux-kernel - Re: [PATCH 3/3][v3] Thermal: do thermal zone update after a cooling device registered

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Date:	Thu, 31 Dec 2015 11:03:50 -0800
From:	Eduardo Valentin <edubezval@...il.com>
To:	Chen Yu <yu.c.chen@...el.com>
Cc:	rui.zhang@...el.com, javi.merino@....com, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH 3/3][v3] Thermal: do thermal zone update after a cooling
 device registered

Hello Chen,

On Fri, Oct 30, 2015 at 04:32:10PM +0800, Chen Yu wrote:
> When a new cooling device is registered, we need to update the
> thermal zone to set the new registered cooling device to a proper
> state.
> 
> This fixes a problem that the system is cool, while the fan devices
> are left running on full speed after boot, if fan device is registered
> after thermal zone device.
> 
> Here is the history of why current patch looks like this:
> https://patchwork.kernel.org/patch/7273041/
> 
> CC: <stable@...r.kernel.org> #3.18+
> Reference:https://bugzilla.kernel.org/show_bug.cgi?id=92431
> Tested-by: Manuel Krause <manuelkrause@...scape.net>
> Tested-by: szegad <szegadlo@...zta.onet.pl>
> Tested-by: prash <prash.n.rao@...il.com>
> Tested-by: amish <ammdispose-arch@...oo.com>
> Reviewed-by: Javi Merino <javi.merino@....com>
> Signed-off-by: Zhang Rui <rui.zhang@...el.com>
> Signed-off-by: Chen Yu <yu.c.chen@...el.com>
> ---
>  drivers/thermal/thermal_core.c | 14 +++++++++++++-
>  include/linux/thermal.h        |  2 ++
>  2 files changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
> index 9aae767..ba08b55 100644
> --- a/drivers/thermal/thermal_core.c
> +++ b/drivers/thermal/thermal_core.c
> @@ -1341,6 +1341,7 @@ int thermal_zone_bind_cooling_device(struct thermal_zone_device *tz,
>  	if (!result) {
>  		list_add_tail(&dev->tz_node, &tz->thermal_instances);
>  		list_add_tail(&dev->cdev_node, &cdev->thermal_instances);
> +		atomic_set(&tz->need_update, 1);
>  	}
>  	mutex_unlock(&cdev->lock);
>  	mutex_unlock(&tz->lock);
> @@ -1450,6 +1451,7 @@ __thermal_cooling_device_register(struct device_node *np,
>  				  const struct thermal_cooling_device_ops *ops)
>  {
>  	struct thermal_cooling_device *cdev;
> +	struct thermal_zone_device *pos = NULL;
>  	int result;
>  
>  	if (type && strlen(type) >= THERMAL_NAME_LENGTH)
> @@ -1494,6 +1496,12 @@ __thermal_cooling_device_register(struct device_node *np,
>  	/* Update binding information for 'this' new cdev */
>  	bind_cdev(cdev);
>  
> +	mutex_lock(&thermal_list_lock);
> +	list_for_each_entry(pos, &thermal_tz_list, node)
> +		if (atomic_cmpxchg(&pos->need_update, 1, 0))
> +			thermal_zone_device_update(pos);
> +	mutex_unlock(&thermal_list_lock);
> +
>  	return cdev;
>  }
>  
> @@ -1826,6 +1834,8 @@ struct thermal_zone_device *thermal_zone_device_register(const char *type,
>  	tz->trips = trips;
>  	tz->passive_delay = passive_delay;
>  	tz->polling_delay = polling_delay;
> +	/* A new thermal zone needs to be updated anyway. */
> +	atomic_set(&tz->need_update, 1);
>  
>  	dev_set_name(&tz->device, "thermal_zone%d", tz->id);
>  	result = device_register(&tz->device);
> @@ -1921,7 +1931,9 @@ struct thermal_zone_device *thermal_zone_device_register(const char *type,
>  	INIT_DELAYED_WORK(&(tz->poll_queue), thermal_zone_device_check);
>  
>  	thermal_zone_device_reset(tz);
> -	thermal_zone_device_update(tz);
> +	/* Update the new thermal zone and mark it as already updated. */
> +	if (atomic_cmpxchg(&tz->need_update, 1, 0))
> +		thermal_zone_device_update(tz);
>  
>  	return tz;
>  
> diff --git a/include/linux/thermal.h b/include/linux/thermal.h
> index 5bcabc7..385d411 100644
> --- a/include/linux/thermal.h
> +++ b/include/linux/thermal.h
> @@ -168,6 +168,7 @@ struct thermal_attr {
>   * @forced_passive:	If > 0, temperature at which to switch on all ACPI
>   *			processor cooling devices.  Currently only used by the
>   *			step-wise governor.
> + * @need_update:	if equals 1, thermal_zone_device_update needs to be invoked.
>   * @ops:	operations this &thermal_zone_device supports
>   * @tzp:	thermal zone parameters
>   * @governor:	pointer to the governor for this thermal zone
> @@ -195,6 +196,7 @@ struct thermal_zone_device {
>  	int emul_temperature;
>  	int passive;
>  	unsigned int forced_passive;
> +	atomic_t need_update;

The only problem I have with the above change is the fact that it does
not touch thermal_zone_device_update() in any place. Please, remember
that thermal_zone_device_update() is an exported function. That means
that anyone can actually call it. And that is what happens today. If you
git grep for it you will see that there are occurrences inside thermal
core and inside thermal drivers. And this change do not take care of
them. Are you sure you don't need to revisit all occurrences?

Shouldn't thermal_zone_device_update() unset the need_update bit, given
it has just updated the zone?

Also, what happens to the logic when external changes happens? Say, we
have writable trip points enabled, and user changes a trip point value?


BR,

>  	struct thermal_zone_device_ops *ops;
>  	struct thermal_zone_params *tzp;
>  	struct thermal_governor *governor;
> -- 
> 1.8.4.2
> 
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