Re: [PATCH V6 XRT Alveo 16/20] fpga: xrt: clock driver

[Lizhi Hou]

On 05/13/2021 08:48 AM, Tom Rix wrote:
> > +
> > +static int get_freq(struct clock *clock, u16 *freq)
> > +{
>
> > +
> > +     /*
> > +      * Multiply both numerator (mul0) and the denominator (div1) with
> > +      * 1000 to account for fractional portion of divider
> > +      */
> > +
> > +     div1 *= 1000;
> > +     div1 += div_frac1;
> > +     div0 *= div1;
> > +     mul0 *= 1000;
> > +     if (div0 == 0) {
> > +             CLOCK_ERR(clock, "clockwiz 0 divider");
>
> This prevents a divide by zero, but returns 0 without setting freq
>
> A -EINVAL should be returned or freq initialized to some default value
Sure.
> > +             return 0;
> > +     }
> > +
> > +     input = mul0 * 100;
> > +     do_div(input, div0);
> > +     *freq = (u16)input;
> > +
> > +     return 0;
> > +}
> > +
> >
> > +
> > +static int clock_verify_freq(struct clock *clock)
> > +{
> > +     u32 lookup_freq, clock_freq_counter, request_in_khz, tolerance;
> > +     int err = 0;
> > +     u16 freq;
> > +
> > +     mutex_lock(&clock->clock_lock);
> > +
> > +     err = get_freq(clock, &freq);
> > +     if (err) {
> > +             xrt_err(clock->xdev, "get freq failed, %d", err);
> > +             goto end;
> > +     }
> > +
> > +     err = get_freq_counter(clock, &clock_freq_counter);
> > +     if (err) {
> > +             xrt_err(clock->xdev, "get freq counter failed, %d", err);
> > +             goto end;
> > +     }
> > +
> > +     lookup_freq = find_matching_freq(freq, frequency_table,
> > + ARRAY_SIZE(frequency_table));
>
> I am running v6 through clang's static analyzer, it shows a problem here
>
> drivers/fpga/xrt/lib/xleaf/clock.c:474:16: warning: 1st function call
> argument is an uninitialized value
>         lookup_freq = find_matching_freq(freq, frequency_table,
>                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> See problem with get_freq above
Sure.

Thanks,
Lizhi
> Tom