Messages in this thread | | | 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 <> | Date | Sun, 25 Dec 2022 12:50:46 +0100 |
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Lähetetty iPhonesta
> Andy Shevchenko <andy.shevchenko@gmail.com> kirjoitti 25.12.2022 kello 12.45: > > > > Lähetetty iPhonesta > >>> Dan Carpenter <error27@gmail.com> kirjoitti 24.12.2022 kello 20.30: >>> >>> On Sat, Dec 24, 2022 at 05:19:27PM +0100, Andy Shevchenko wrote: >>> >>> >>> Lähetetty iPhonesta >>> >>>> Dan Carpenter <error27@gmail.com> 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@intel.com> >>>> | Reported-by: Dan Carpenter <error27@gmail.com> >>>> >>>> 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? > > The point is that semantically the / is better in case this code will ever support more than two banks of pins.
On top of that it’s paired with 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 >>>>
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