On Fri, Sep 14, 2018 at 10:47 PM Nathan Chancellor
<natechancellor@xxxxxxxxx> wrote:
>
> Clang warns that 'interleaving' is assigned to itself in this function.
>
> drivers/media/dvb-frontends/dib7000p.c:1874:15: warning: explicitly
> assigning value of variable of type 'int' to itself [-Wself-assign]
> interleaving = interleaving;
> ~~~~~~~~~~~~ ^ ~~~~~~~~~~~~
> 1 warning generated.
>
> It's correct. Just removing the self-assignment would sufficiently hide
> the warning but all of this code is dead because 'tmp' is zero due to
> being multiplied by zero. This doesn't appear to be an issue with
> dib8000, which this code was copied from in commit 041ad449683b
> ("[media] dib7000p: Add DVBv5 stats support").
>
> Reported-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> Signed-off-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
> ---
> drivers/media/dvb-frontends/dib7000p.c | 10 ++--------
> 1 file changed, 2 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/media/dvb-frontends/dib7000p.c b/drivers/media/dvb-frontends/dib7000p.c
> index 58387860b62d..25843658fc68 100644
> --- a/drivers/media/dvb-frontends/dib7000p.c
> +++ b/drivers/media/dvb-frontends/dib7000p.c
> @@ -1800,9 +1800,8 @@ static u32 dib7000p_get_time_us(struct dvb_frontend *demod)
Something looks wrong here (with this function). The patch is no
functional change, since as you point out `interleaving` is
initialized to 0, then never updated before read, but I think there's
an underlying bug here that should be fixed differently. Thanks for
the patch though, as it does raise the question.
dib7000p_get_time_us has this comment above it:
1798 /* FIXME: may require changes - this one was borrowed from
dib8000 */
Wondering if it has the same bug, it seems it does not:
drivers/media/dvb-frontends/dib8000.c#dib8000_get_time_us():3986
dib8000_get_time_us() seems to loop over multiple layers, and then
assigns interleaving to the final layers interleaving (that looks like
loop invariant code to me).
Mauro, should dib7000p_get_time_us() use c->layer[???].interleaving?
I don't see a single reference to `layer` in
drivers/media/dvb-frontends/dib7000p.c.
> {
> struct dtv_frontend_properties *c = &demod->dtv_property_cache;
> u64 time_us, tmp64;
> - u32 tmp, denom;
> - int guard, rate_num, rate_denum = 1, bits_per_symbol;
> - int interleaving = 0, fft_div;
> + u32 denom;
> + int guard, rate_num, rate_denum = 1, bits_per_symbol, fft_div;
>
> switch (c->guard_interval) {
> case GUARD_INTERVAL_1_4:
> @@ -1871,8 +1870,6 @@ static u32 dib7000p_get_time_us(struct dvb_frontend *demod)
> break;
> }
>
> - interleaving = interleaving;
> -
> denom = bits_per_symbol * rate_num * fft_div * 384;
>
> /* If calculus gets wrong, wait for 1s for the next stats */
> @@ -1887,9 +1884,6 @@ static u32 dib7000p_get_time_us(struct dvb_frontend *demod)
> time_us += denom / 2;
> do_div(time_us, denom);
>
> - tmp = 1008 * 96 * interleaving;
> - time_us += tmp + tmp / guard;
> -
> return time_us;
> }
>
> --
> 2.18.0
>
--
Thanks,
~Nick Desaulniers
