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: Sat Dec 24 2022 - 11:24:45 EST




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.


> 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 }
>
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