linux-kernel - Re: [PATCH v3 3/4] thermal: core: genetlink support for events/cmd/sampling

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Date:   Mon, 6 Jul 2020 09:04:07 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Zhang Rui <rui.zhang@...el.com>
Cc:     srinivas.pandruvada@...ux.intel.com, rkumbako@...eaurora.org,
        amit.kucheria@...aro.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH v3 3/4] thermal: core: genetlink support for
 events/cmd/sampling

On 05/07/2020 08:03, Zhang Rui wrote:
> On Fri, 2020-07-03 at 10:53 +0200, Daniel Lezcano wrote:
>> Initially the thermal framework had a very simple notification
>> mechanism to send generic netlink messages to the userspace.
>>
>> The notification function was never called from anywhere and the
>> corresponding dead code was removed. It was probably a first attempt
>> to introduce the netlink notification.
>>
>> At LPC2018, the presentation "Linux thermal: User kernel interface",
>> proposed to create the notifications to the userspace via a kfifo.
>>
>> The advantage of the kfifo is the performance. It is usually used
>> from
>> a 1:1 communication channel where a driver captures data and sends it
>> as fast as possible to a userspace process.
>>
>> The drawback is that only one process uses the notification channel
>> exclusively, thus no other process is allowed to use the channel to
>> get temperature or notifications.
>>
>> This patch defines a generic netlink API to discover the current
>> thermal setup and adds event notifications as well as temperature
>> sampling. As any genetlink protocol, it can evolve and the versioning
>> allows to keep the backward compatibility.
>>
>> In order to prevent the user from getting flooded with data on a
>> single channel, there are two multicast channels, one for the
>> temperature sampling when the thermal zone is updated and another one
>> for the events, so the user can get the events only without the
>> thermal zone temperature sampling.
>>
>> Also, a list of commands to discover the thermal setup is added and
>> can be extended when needed.
>>
>> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
>> ---

[ ... ]

>> +static int thermal_genl_event_cdev_update(struct param *p)
>> +{
>> +	if (nla_put_u32(p->msg, THERMAL_GENL_ATTR_CDEV_ID,
>> +			p->cdev_id) ||
>> +	    nla_put_u32(p->msg, THERMAL_GENL_ATTR_CDEV_CUR_STATE,
>> +			p->cdev_state) ||
>> +	    nla_put_u32(p->msg, THERMAL_GENL_ATTR_CDEV_MAX_STATE,
>> +			p->cdev_max_state))
>> +		return -EMSGSIZE;
>> +
>> +	return 0;
>> +}
> 
>> +int thermal_notify_cdev_update(int cdev_id, int cdev_state)
>>> +{
>>> +	struct param p = { .cdev_id = cdev_id, .cdev_state = cdev_state
>>> };
>>
> 
> .cdev_max_state is not set here.
> I think we need to add a second parameter for cdev_max_state when
> invoking thermal_nofify_cdev_update().

I've been trying to figure when the max state is changed and the
notification for the max state is less straightforward than the current
state.

Actually merging both changes is not a good idea.

It would be preferable to add later the max state change notification
and keep set current state as before, except changing the function and
attributes to cdev_state_update.

Sounds good ?


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