Messages in this thread | | | Date | Tue, 27 Dec 2022 20:46:13 +0300 | From | Dan Carpenter <> | Subject | Re: drivers/gpio/gpio-exar.c:52 exar_offset_to_sel_addr() warn: replace divide condition 'pin / 8' with 'pin >= 8' |
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On Sun, Dec 25, 2022 at 12:50:46PM +0100, Andy Shevchenko wrote: > > > 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 noticed that, but it's a common bug though that a lot of people accidentally write if (pin / 8) when if ((pin % 8) == 0) is intended.
For example:
drivers/rtc/rtc-m48t59.c 132 M48T59_WRITE((bin2bcd(tm->tm_mon + 1) & 0x1F), M48T59_MONTH); 133 M48T59_WRITE(bin2bcd(year % 100), M48T59_YEAR); 134 135 if (pdata->type == M48T59RTC_TYPE_M48T59 && (year / 100)) ^^^^^^^^^^ This code is pretty clearly an example of where people accidentally uses / to mean "divides cleanly". (I have not patched or reported this code, btw so if anyone wants an easy patch to send it's available).
136 val = (M48T59_WDAY_CEB | M48T59_WDAY_CB); 137 val |= (bin2bcd(tm->tm_wday) & 0x07); 138 M48T59_WRITE(val, M48T59_WDAY);
regards, dan carpenter
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