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

Nicolin Chen
2018-10-25T01:33:58Z

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
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