Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Feedback-ID: i8771445c:Fastmail
Date:   Wed, 14 Jun 2023 12:28:14 +0200
From:   Maxime Ripard <maxime@cerno.tech>
To:     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
Subject: Re: [PATCH v2 1/2] clk: composite: Fix handling of high clock rates
Message-ID: <6nihw4k2vdtmjpvbei5ahb7cmtmuyi2w5m4pwhjrmdqi2yp7v6@vdpg5kwa7trl>
References: <20230526171057.66876-1-sebastian.reichel@collabora.com>
 <20230526171057.66876-2-sebastian.reichel@collabora.com>
 <2f3328c4be9db6feef2cc662ede70f92.sboyd@kernel.org>
 <7s2xdk43a2lhyezgj6bbwxaekbtgym2rin7t432m4pos4j6v74@qaxm3htjak4a>
 <86d58c6b131028a71964a0bcb135f01f.sboyd@kernel.org>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha512;
        protocol="application/pgp-signature"; boundary="rvbzj4d27cgjtg4p"
Content-Disposition: inline
In-Reply-To: <86d58c6b131028a71964a0bcb135f01f.sboyd@kernel.org>
Precedence: bulk


--rvbzj4d27cgjtg4p
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Tue, Jun 13, 2023 at 11:25:12AM -0700, Stephen Boyd wrote:
> 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-composit=
e.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=
 clk_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.r=
ate;
> > > > +                       else
> > > > +                               rate_diff =3D tmp_req.rate - req->r=
ate;
> > >=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?
>=20
> Good point. I haven't looked to see if any drivers are using the
> max_rate directly. Hopefully they aren't.

I had a quick grep for 'req->max_rate' under drivers/clk and there's no
driver using abs on that field.

Maxime

--rvbzj4d27cgjtg4p
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----

iHUEABYKAB0WIQRcEzekXsqa64kGDp7j7w1vZxhRxQUCZImWPgAKCRDj7w1vZxhR
xWqqAQDtRJu+7X2t9w8kMiWSgFzQ9bh/myP2kVaGllLA7Ryp4gEA8nCo9oZhnPp0
paQV2Ot+629yys6nYCty3z7AzXB2Jw4=
=Dq2e
-----END PGP SIGNATURE-----

--rvbzj4d27cgjtg4p--