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Subject: Re: drivers/gpio/gpio-exar.c:52 exar_offset_to_sel_addr() warn: replace divide condition 'pin / 8' with 'pin >= 8'
From:   Andy Shevchenko <andy.shevchenko@gmail.com>
In-Reply-To: <202212181140.EAWl7FKx-lkp@intel.com>
Date:   Sat, 24 Dec 2022 17:19:27 +0100
Cc:     oe-kbuild@lists.linux.dev, Qingtao Cao <qingtao.cao.au@gmail.com>,
        lkp@intel.com, oe-kbuild-all@lists.linux.dev,
        linux-kernel@vger.kernel.org, Bartosz Golaszewski <brgl@bgdev.pl>
Content-Transfer-Encoding: quoted-printable
Message-Id: <3D147284-AF8C-4414-9BE1-C83032B6C15D@gmail.com>
References: <202212181140.EAWl7FKx-lkp@intel.com>
To:     Dan Carpenter <error27@gmail.com>
Precedence: bulk


L=C3=A4hetetty iPhonesta

> Dan Carpenter <error27@gmail.com> kirjoitti 23.12.2022 kello 11.54:
>=20
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git=
 master
> head:   f9ff5644bcc04221bae56f922122f2b7f5d24d62
> commit: 5134272f9f3f71d4e1f3aa15cb09321af49b3646 gpio: exar: access MPIO r=
egisters on cascaded chips
> config: ia64-randconfig-m031-20221218
> compiler: ia64-linux-gcc (GCC) 12.1.0
>=20
> If you fix the issue, kindly add following tag where applicable
> | Reported-by: kernel test robot <lkp@intel.com>
> | Reported-by: Dan Carpenter <error27@gmail.com>
>=20
> smatch warnings:
> drivers/gpio/gpio-exar.c:52 exar_offset_to_sel_addr() warn: replace divide=
 condition 'pin / 8' with 'pin >=3D 8'
> drivers/gpio/gpio-exar.c:62 exar_offset_to_lvl_addr() warn: replace divide=
 condition 'pin / 8' with 'pin >=3D 8'
>=20


I don=E2=80=99t think this is a good advice. If we want to limit that, we ne=
ed to check also upper limit. But. The GPIO framework does that. So, changin=
g / to >=3D is bogus.


> vim +52 drivers/gpio/gpio-exar.c
>=20
> 696868d0a79c21 Bartosz Golaszewski 2020-09-30  47  static unsigned int
> 696868d0a79c21 Bartosz Golaszewski 2020-09-30  48  exar_offset_to_sel_addr=
(struct exar_gpio_chip *exar_gpio, unsigned int offset)
> 696868d0a79c21 Bartosz Golaszewski 2020-09-30  49  {
> 5134272f9f3f71 Qingtao Cao         2022-09-02  50      unsigned int pin =3D=
 exar_gpio->first_pin + (offset % 16);
> 5134272f9f3f71 Qingtao Cao         2022-09-02  51      unsigned int cascad=
ed =3D offset / 16;
> 5134272f9f3f71 Qingtao Cao         2022-09-02 @52      unsigned int addr =3D=
 pin / 8 ? EXAR_OFFSET_MPIOSEL_HI : EXAR_OFFSET_MPIOSEL_LO;
>=20
> Why not change this to pin > 8 instead.  Comparisons are faster than
> divide ops.  Way more readable too.
>=20
> 5134272f9f3f71 Qingtao Cao         2022-09-02  53 =20
> 5134272f9f3f71 Qingtao Cao         2022-09-02  54      return addr + (casc=
aded ? exar_gpio->cascaded_offset : 0);
> 696868d0a79c21 Bartosz Golaszewski 2020-09-30  55  }
> 696868d0a79c21 Bartosz Golaszewski 2020-09-30  56 =20
> 696868d0a79c21 Bartosz Golaszewski 2020-09-30  57  static unsigned int
> 696868d0a79c21 Bartosz Golaszewski 2020-09-30  58  exar_offset_to_lvl_addr=
(struct exar_gpio_chip *exar_gpio, unsigned int offset)
> 696868d0a79c21 Bartosz Golaszewski 2020-09-30  59  {
> 5134272f9f3f71 Qingtao Cao         2022-09-02  60      unsigned int pin =3D=
 exar_gpio->first_pin + (offset % 16);
> 5134272f9f3f71 Qingtao Cao         2022-09-02  61      unsigned int cascad=
ed =3D offset / 16;
> 5134272f9f3f71 Qingtao Cao         2022-09-02 @62      unsigned int addr =3D=
 pin / 8 ? EXAR_OFFSET_MPIOLVL_HI : EXAR_OFFSET_MPIOLVL_LO;
> 5134272f9f3f71 Qingtao Cao         2022-09-02  63 =20
> 5134272f9f3f71 Qingtao Cao         2022-09-02  64      return addr + (casc=
aded ? exar_gpio->cascaded_offset : 0);
> 696868d0a79c21 Bartosz Golaszewski 2020-09-30  65  }
>=20
> --=20
> 0-DAY CI Kernel Test Service
> https://01.org/lkp
>=20