linux-kernel - Re: [PATCH] thermal: core: Send a sysfs notification on trip points

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Message-ID: <62f5e0d0-155a-7520-cb1b-2113a2b711b3@linaro.org>
Date:   Mon, 6 Apr 2020 11:45:10 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Vincent Whitchurch <vincent.whitchurch@...s.com>
Cc:     "rui.zhang@...el.com" <rui.zhang@...el.com>,
        "amit.kucheria@...durent.com" <amit.kucheria@...durent.com>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] thermal: core: Send a sysfs notification on trip points

On 06/04/2020 09:45, Vincent Whitchurch wrote:
> On Fri, Apr 03, 2020 at 05:26:39PM +0200, Daniel Lezcano wrote:
>> On 03/04/2020 16:40, Vincent Whitchurch wrote:
>>> Normally sysfs_notify() is used to notify userspace that the
>>> value of the sysfs file has changed, but in this case it's
>>> being used on a sysfs file whose value never changes.  I don't
>>> know if there are other drivers that do something similar.
>>
>> I think so:
>>
>> eg.
>>
>> drivers/hwmon/adt7x10.c: sysfs_notify(&dev->kobj, NULL,
>> "temp1_max_alarm"); drivers/hwmon/adt7x10.c:
>> sysfs_notify(&dev->kobj, NULL, "temp1_min_alarm");
>> drivers/hwmon/adt7x10.c: sysfs_notify(&dev->kobj, NULL,
>> "temp1_crit_alarm");
>>
>> drivers/hwmon/abx500.c: sysfs_notify(&data->pdev->dev.kobj, NULL,
>> alarm_node); drivers/hwmon/abx500.c:
>> sysfs_notify(&data->pdev->dev.kobj, NULL, alarm_node);
>>
>> drivers/hwmon/stts751.c: sysfs_notify(&priv->dev->kobj, NULL,
>> "temp1_max_alarm"); drivers/hwmon/stts751.c:
>> sysfs_notify(&priv->dev->kobj, NULL, "temp1_min_alarm");
>>
>> There are also some other places I believe they are doing the
>> same like:
>>
>> drivers/md/md.c: sysfs_notify(&mddev->kobj, NULL,
>> "sync_completed"); drivers/md/md.c: sysfs_notify(&mddev->kobj,
>> NULL, "degraded");
>
> AFAICS all these drivers (including the hwmon ones) use
> sysfs_notify() to notify that the value of the sysfs file has
> changed, unlike your proposed patch.

Sorry, I don't have the same understanding:

drivers/hwmon/adt7x10.c:

 - receives an interrupt because one of the programmed temperature is
reached
 - reads the status to know which one and sends a sysfs notification

drivers/hwmon/stts751.c:

 - receives an I2C alert message, checks if it is a temperature alert
and then sends a sysfs notification

drivers/hwmon/abx500:

 - This one is probably sending a notification on a change

The documentation also is giving the semantic for sysfs_notify for
certain sysfs nodes:

Documentation/misc-devices/apds990x.txt:             sysfs_notify
called when threshold interrupt occurs
Documentation/misc-devices/bh1770glc.txt:            sysfs_notify
called when threshold interrupt occurs

AFAICT, it is a matter of documenting the notification for
trip_point_*_temp.


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