Re: [PATCH v3 1/5] hwmon: (core) Inherit power properties to hdev

From: linux@roeck-us.net
To: Nicolin Chen <nicoleotsuka@gmail.com>
Cc: jdelvare@suse.com, linux-hwmon@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 1/5] hwmon: (core) Inherit power properties to hdev
Date: Thu, 25 Oct 2018 06:55:31 +0000	[thread overview]
Message-ID: <20181025065531.Horde.JhVAJU3eOlwYcSJ57tV4I5-@cp2.active-venture.com> (raw)
In-Reply-To: <20181025013349.GA7569@Asurada-Nvidia.nvidia.com>

Quoting Nicolin Chen <nicoleotsuka@gmail.com>:

> On Wed, Oct 24, 2018 at 06:01:16PM -0700, Nicolin Chen wrote:
>> On Thu, Oct 25, 2018 at 12:13:01AM +0000, linux@roeck-us.net wrote:
>>
>> > > +	if (dev) {
>> > > +		hdev->driver = dev->driver;
>> > > +		hdev->power = dev->power;
>> > > +		hdev->pm_domain = dev->pm_domain;
>> > > +		hdev->of_node = dev->of_node;
>> > > +	}
>> >
>> > We'l need to dig into this more; I suspect it may be  
>> inappropriate to do this.
>> > With this change, every hwmon driver supporting (runtime ?) suspend/resume
>> > will have the problem worked around in #5, and that just seems wrong.
>>
>> Hmm..that's true...thanks for catching it.
>>
>> Actually I am not sure the reason of having a child device in
>> the core, but could we use the parent dev pointer in the hwmon
>> core as hwmon_dev upon confirming parent dev pointer != NULL?
>
> I just noticed that it is used to link to hwmon class. So this

Exactly.

> won't work then. I guess it'd be safer to ignore the problem of
> the power node, i.e. using parent dev pointer for pm runtime.
>
It might be worthwhile looking up how other virtal devices handle
this problem. Maybe the hwmon code could have its own suspend/resume
callbacks. Not sure how to make that work, though, and what those
callbacks would (have to) do.

Guenter

> Thanks
> Nicolin
>
>> The problem here is that the power directory under each hwmon
>> directory is tied to the hwmon_dev pointer, not to the parent
>> dev pointer, and the hwmon core creates all sysfs nodes based
>> on the child node. So those nodes under power directory won't
>> be valid unless we copy all pm information, especially PM ops.
>>
>> There is an option of ignoring this problem though, while all
>> hwmon drivers will need to be careful of mixing using the dev
>> pointers. So it'd be a lot of easier if we could just use the
>> original dev pointer in the core since we mainly just need to
>> create sysfs nodes.
>>
>> Another way of doing this might be to pass down the PM pointer
>> via _info structure instead of linking it to the parent driver,
>> which then will forbid all hwmon drivers having its own PM ops
>> callbacks -- the very opposite way of this patch, and it does
>> not sound fully reasonable and feasible to me...
>>
>> What do you think about?
>>
>> Thanks
>> Nicolin