Re: drivers/gpio/gpio-exar.c:52 exar_offset_to_sel_addr() warn: replace divide condition 'pin / 8' with 'pin >= 8'

From: Dan Carpenter
Date: Sat Dec 24 2022 - 14:31:01 EST


On Sat, Dec 24, 2022 at 05:19:27PM +0100, Andy Shevchenko wrote:
>
>
> Lähetetty iPhonesta
>
> > Dan Carpenter <error27@xxxxxxxxx> kirjoitti 23.12.2022 kello 11.54:
> >
> > tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 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
> >
> > If you fix the issue, kindly add following tag where applicable
> > | Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > | Reported-by: Dan Carpenter <error27@xxxxxxxxx>
> >
> > smatch warnings:
> > drivers/gpio/gpio-exar.c:52 exar_offset_to_sel_addr() warn: replace divide condition 'pin / 8' with 'pin >= 8'
> > drivers/gpio/gpio-exar.c:62 exar_offset_to_lvl_addr() warn: replace divide condition 'pin / 8' with 'pin >= 8'
> >
>
>
>
> I don’t 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 >= is bogus.


How is checking pin / 8 not mathematically equivalent to pin >= 8?

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)).

regards,
dan carpenter

>
>
> > vim +52 drivers/gpio/gpio-exar.c
> >
> > 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 = exar_gpio->first_pin + (offset % 16);
> > 5134272f9f3f71 Qingtao Cao 2022-09-02 51 unsigned int cascaded = offset / 16;
> > 5134272f9f3f71 Qingtao Cao 2022-09-02 @52 unsigned int addr = pin / 8 ? EXAR_OFFSET_MPIOSEL_HI : EXAR_OFFSET_MPIOSEL_LO;
> >
> > Why not change this to pin > 8 instead. Comparisons are faster than
> > divide ops. Way more readable too.
> >
> > 5134272f9f3f71 Qingtao Cao 2022-09-02 53
> > 5134272f9f3f71 Qingtao Cao 2022-09-02 54 return addr + (cascaded ? exar_gpio->cascaded_offset : 0);
> > 696868d0a79c21 Bartosz Golaszewski 2020-09-30 55 }
> > 696868d0a79c21 Bartosz Golaszewski 2020-09-30 56
> > 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 = exar_gpio->first_pin + (offset % 16);
> > 5134272f9f3f71 Qingtao Cao 2022-09-02 61 unsigned int cascaded = offset / 16;
> > 5134272f9f3f71 Qingtao Cao 2022-09-02 @62 unsigned int addr = pin / 8 ? EXAR_OFFSET_MPIOLVL_HI : EXAR_OFFSET_MPIOLVL_LO;
> > 5134272f9f3f71 Qingtao Cao 2022-09-02 63
> > 5134272f9f3f71 Qingtao Cao 2022-09-02 64 return addr + (cascaded ? exar_gpio->cascaded_offset : 0);
> > 696868d0a79c21 Bartosz Golaszewski 2020-09-30 65 }
> >
> > --
> > 0-DAY CI Kernel Test Service
> > https://01.org/lkp
> >