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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: <Y6dTX2wx/SXlswGC@kadam>
Date:   Sun, 25 Dec 2022 12:45:12 +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: <F701A496-22A6-4E3B-B3CB-E5BCF4C30502@gmail.com>
References: <202212181140.EAWl7FKx-lkp@intel.com> <3D147284-AF8C-4414-9BE1-C83032B6C15D@gmail.com> <Y6dTX2wx/SXlswGC@kadam>
To:     Dan Carpenter <error27@gmail.com>
Precedence: bulk


L=C3=A4hetetty iPhonesta

> Dan Carpenter <error27@gmail.com> kirjoitti 24.12.2022 kello 20.30:
>=20
>> On Sat, Dec 24, 2022 at 05:19:27PM +0100, Andy Shevchenko wrote:
>>=20
>>=20
>> L=C3=A4hetetty iPhonesta
>>=20
>>> 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.g=
it master
>>> head:   f9ff5644bcc04221bae56f922122f2b7f5d24d62
>>> commit: 5134272f9f3f71d4e1f3aa15cb09321af49b3646 gpio: exar: access MPIO=
 registers 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 divi=
de condition 'pin / 8' with 'pin >=3D 8'
>>> drivers/gpio/gpio-exar.c:62 exar_offset_to_lvl_addr() warn: replace divi=
de condition 'pin / 8' with 'pin >=3D 8'
>>>=20
>>=20
>>=20
>>=20
>> I don=E2=80=99t think this is a good advice. If we want to limit that, we=
 need
>> to check also upper limit. But. The GPIO framework does that. So,
>> changing / to >=3D is bogus.
>=20
>=20
> How is checking pin / 8 not mathematically equivalent to pin >=3D 8?

The point is that semantically the / is better in case this code will ever s=
upport more than two banks of pins.


> I don't understand this code at all.  The divide is inscrutable  Is it
> storing something in in the lower 3 bits and something in bit 4?  In
> that case it might be nicer to just check (pin & BIT(4)).
>=20
> regards,
> dan carpenter
>=20
>>=20
>>=20
>>> 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_ad=
dr(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 casc=
aded =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 + (ca=
scaded ? 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_ad=
dr(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 casc=
aded =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 + (ca=
scaded ? 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