linux-kernel - Re: [PATCH 6.6] thermal/of: Fix mask mismatch when no trips subnode

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Message-ID: <2025071407-fender-passcode-b53c@gregkh>
Date: Mon, 14 Jul 2025 15:04:29 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Hsin-Te Yuan <yuanhsinte@...omium.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Amit Kucheria <amitk@...nel.org>, Zhang Rui <rui.zhang@...el.com>,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH 6.6] thermal/of: Fix mask mismatch when no trips subnode

On Mon, Jul 14, 2025 at 08:36:29PM +0800, Hsin-Te Yuan wrote:
> On Thu, Jul 10, 2025 at 9:33 PM Greg KH <gregkh@...uxfoundation.org> wrote:
> >
> > On Mon, Jul 07, 2025 at 06:27:10PM +0800, Hsin-Te Yuan wrote:
> > > After commit 725f31f300e3 ("thermal/of: support thermal zones w/o trips
> > > subnode") was backported on 6.6 stable branch as commit d3304dbc2d5f
> > > ("thermal/of: support thermal zones w/o trips subnode"), thermal zones
> > > w/o trips subnode still fail to register since `mask` argument is not
> > > set correctly. When number of trips subnode is 0, `mask` must be 0 to
> > > pass the check in `thermal_zone_device_register_with_trips()`.
> > >
> > > Set `mask` to 0 when there's no trips subnode.
> > >
> > > Signed-off-by: Hsin-Te Yuan <yuanhsinte@...omium.org>
> > > ---
> > >  drivers/thermal/thermal_of.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/thermal/thermal_of.c b/drivers/thermal/thermal_of.c
> > > index 0f520cf923a1e684411a3077ad283551395eec11..97aeb869abf5179dfa512dd744725121ec7fd0d9 100644
> > > --- a/drivers/thermal/thermal_of.c
> > > +++ b/drivers/thermal/thermal_of.c
> > > @@ -514,7 +514,7 @@ static struct thermal_zone_device *thermal_of_zone_register(struct device_node *
> > >       of_ops->bind = thermal_of_bind;
> > >       of_ops->unbind = thermal_of_unbind;
> > >
> > > -     mask = GENMASK_ULL((ntrips) - 1, 0);
> > > +     mask = ntrips ? GENMASK_ULL((ntrips) - 1, 0) : 0;
> >
> > Meta-comment, I hate ? : lines in C, especially when they are not
> > needed, like here.  Spell this out, with a real if statement please, so
> > that we can read and easily understand what is going on.
> >
> I will change this in v2 if we end up going with this solution.
> 
> > That being said, I agree with Rafael, let's do whatever is in mainline
> > instead.  Fix it the same way it was fixed there by backporting the
> > relevant commits.
> >
> > thanks,
> >
> > greg k-h
> 
> `mask` is removed in 83c2d444ed9d ("thermal: of: Set
> THERMAL_TRIP_FLAG_RW_TEMP directly"), which needs 5340f7647294
> ("thermal: core: Add flags to struct thermal_trip"). I think it's
> beyond a fix to introduce this. Also, there were several conflicts
> when I tried to cherry-pick 5340f7647294. Compared to a simple
> solution like setting `mask` to 0, I don't think it's worthwhile and
> safe to cherry-pick all the dependencies.

Remember, every patch you add to the tree that is NOT upstream, will
almost always cause problems later on, if not immediately (we have a
lousy track record of one-off-patches.)  Also this prevents future
upstream changes from being able to be applied to the tree.

And as you will now be responsible for maintaining this for the next 3-4
years, do whatever possible to make it easy to keep alive properly.

thanks,

greg k-h