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Subject: Re: [PATCH v2 1/2] clk: composite: Fix handling of high clock rates
From:   Stephen Boyd <sboyd@kernel.org>
Cc:     Michael Turquette <mturquette@baylibre.com>,
        Sebastian Reichel <sebastian.reichel@collabora.com>,
        linux-clk@vger.kernel.org, linux-kernel@vger.kernel.org,
        Christopher Obbard <chris.obbard@collabora.com>,
        David Laight <David.Laight@aculab.com>, kernel@collabora.com,
        stable@vger.kernel.org
To:     Maxime Ripard <maxime@cerno.tech>
Date:   Tue, 13 Jun 2023 11:25:12 -0700
User-Agent: alot/0.10
Precedence: bulk

Quoting Maxime Ripard (2023-06-13 05:14:25)
> On Mon, Jun 12, 2023 at 05:10:35PM -0700, Stephen Boyd wrote:
> > Quoting Sebastian Reichel (2023-05-26 10:10:56)
> > > diff --git a/drivers/clk/clk-composite.c b/drivers/clk/clk-composite.c
> > > index edfa94641bbf..66759fe28fad 100644
> > > --- a/drivers/clk/clk-composite.c
> > > +++ b/drivers/clk/clk-composite.c
> > > @@ -119,7 +119,10 @@ static int clk_composite_determine_rate(struct c=
lk_hw *hw,
> > >                         if (ret)
> > >                                 continue;
> > > =20
> > > -                       rate_diff =3D abs(req->rate - tmp_req.rate);
> > > +                       if (req->rate >=3D tmp_req.rate)
> > > +                               rate_diff =3D req->rate - tmp_req.rat=
e;
> > > +                       else
> > > +                               rate_diff =3D tmp_req.rate - req->rat=
e;
> >=20
> > This problem is widespread
> >=20
> >  $ git grep abs\(.*- -- drivers/clk/ | wc -l
> >  52
> >=20
> > so we may have a bigger problem here. Maybe some sort of coccinelle
> > script or smatch checker can be written to look for abs() usage with an
> > unsigned long type or a subtraction expression. This may also be worse
> > after converting drivers to clk_hw_forward_rate_request() and
> > clk_hw_init_rate_request() because those set the rate to ULONG_MAX.
> > +Maxime for that as an FYI.
>=20
> We set max_rate to ULONG_MAX in those functions, and I don't think we
> have a lot of driver that will call clk_round_rate on the max rate, so
> we should be somewhat ok?

Good point. I haven't looked to see if any drivers are using the
max_rate directly. Hopefully they aren't.