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

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Message-ID: <20181025013349.GA7569@Asurada-Nvidia.nvidia.com>
Date:   Wed, 24 Oct 2018 18:33:50 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     linux@...ck-us.net
Cc:     jdelvare@...e.com, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/5] hwmon: (core) Inherit power properties to hdev

On Wed, Oct 24, 2018 at 06:01:16PM -0700, Nicolin Chen wrote:
> On Thu, Oct 25, 2018 at 12:13:01AM +0000, linux@...ck-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
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.

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