On Wed, Dec 13, 2023 at 01:40:54PM +0200, Tomi Valkeinen wrote:
> On 13/12/2023 13:23, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@xxxxxxxx>
> >
> > With clang-16, building without COMMON_CLK triggers a range check on
> > udelay() because of a constant division-by-zero calculation:
> >
> > ld.lld: error: undefined symbol: __bad_udelay
> >>>> referenced by mt9m114.c
> >>>> drivers/media/i2c/mt9m114.o:(mt9m114_power_on) in archive vmlinux.a
> >
> > In this configuration, the driver already fails to probe, before
> > this function gets called, so it's enough to suppress the assertion.
> >
> > Do this by using fsleep(), which turns long delays into sleep() calls
> > in place of the link failure.
> >
> > This is probably a good idea regardless to avoid overly long dynamic
> > udelay() calls on a slow clock.
> >
> > Cc: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> > Fixes: 24d756e914fc ("media: i2c: Add driver for onsemi MT9M114 camera sensor")
> > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> > ---
> > drivers/media/i2c/mt9m114.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/media/i2c/mt9m114.c b/drivers/media/i2c/mt9m114.c
> > index 0a22f328981d..68adaecaf481 100644
> > --- a/drivers/media/i2c/mt9m114.c
> > +++ b/drivers/media/i2c/mt9m114.c
> > @@ -2116,7 +2116,7 @@ static int mt9m114_power_on(struct mt9m114 *sensor)
> > duration = DIV_ROUND_UP(2 * 50 * 1000000, freq);
> >
> > gpiod_set_value(sensor->reset, 1);
> > - udelay(duration);
> > + fsleep(duration);
> > gpiod_set_value(sensor->reset, 0);
> > } else {
> > /*
>
> I think this is fine, so:
>
> Reviewed-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
>
> But: If we don't have COMMON_CLK (or rather, I think, HAVE_CLK), the
> freq will be zero at compile time. So won't the compiler give a warning
> for the DIV_ROUND_UP() call?
>
> Interestingly, for me, this doesn't give a div-by-zero warning:
>
> int x;
> int y = 0;
> x = DIV_ROUND_UP(10, y);
>
> but this does:
>
> int x;
> const int y = 0;
> x = DIV_ROUND_UP(10, y);
>
> And looks like this gives the warning too:
>
> int x;
> const int y = 0;
> if (y)
> x = DIV_ROUND_UP(10, y);
>
> So, I think, the code in the driver could fail to compile at some later
> point, if the compiler warnings are improved (?), or if someone adds a
> 'const' in front of 'long freq = clk_get_rate(sensor->clk);' line.
>
> Maybe worry about that if it actually happens =).
Maybe :-) I would be tempted to make VIDEO_CAMERA_SENSOR depend on
COMMON_CLK.
--
Regards,
Laurent Pinchart
