Re: [alsa-devel] [PATCH 1/2] ASoC: codec: wm9860: avoid maybe-uninitialized warning

[Daniel Baluta]

On Fri, Apr 21, 2017 at 5:46 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote:
> On Fri, Apr 21, 2017 at 3:07 PM, Daniel Baluta <daniel.baluta@xxxxxxx> wrote:
>> The new PLL configuration code triggers a harmless warning:
>>
>> sound/soc/codecs/wm8960.c: In function 'wm8960_configure_clocking':
>> sound/soc/codecs/wm8960.c:735:3: error: 'best_freq_out' may be used
>> uninitialized in this function [-Werror=maybe-uninitialized]
>>    wm8960_set_pll(codec, freq_in, best_freq_out);
>>    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> sound/soc/codecs/wm8960.c:699:12: note: 'best_freq_out' was declared
>> here
>>
>> Fixes: 84fdc00d519f ("ASoC: codec: wm9860: Refactor PLL out freq search")
>> Fixes: 303e8954af8d ("ASoC: codec: wm8960: Stop when a matching PLL freq is found")
>> Suggested-by: Arnd Bergmann <arnd@xxxxxxxx>
>> Signed-off-by: Daniel Baluta <daniel.baluta@xxxxxxx>
>> ---
>> Arnd,
>>
>> I agree that your code was more both humans and gcc anyhow
>> for consistency with wm8960_configure_sysclk function I preferred
>> to keep the "if(..) break" statements.
>
> How about changing both functions the same way then?

I've tried but I couldn't find any solution. For clarity here is how
the code actually looks like.

The git diff is a little bit misleading. Here is how wm8960_configure_pll code
looks like:

https://pastebin.com/naGdVNQz

static
int wm8960_configure_pll(struct snd_soc_codec *codec, int freq_in,
                      int *sysclk_idx, int *dac_idx, int *bclk_idx)
{
       struct wm8960_priv *wm8960 = snd_soc_codec_get_drvdata(codec);
       int sysclk, bclk, lrclk, freq_out;
       int diff, closest, best_freq_out;
       int i, j, k;

       bclk = wm8960->bclk;
       lrclk = wm8960->lrclk;
       closest = freq_in;

       best_freq_out = -EINVAL;
       *sysclk_idx = *dac_idx = *bclk_idx = -1;

       for (i = 0; i < ARRAY_SIZE(sysclk_divs); ++i) {
              if (sysclk_divs[i] == -1)
                     continue;
              for (j = 0; j < ARRAY_SIZE(dac_divs); ++j) {
                     sysclk = lrclk * dac_divs[j];
                     freq_out = sysclk * sysclk_divs[i];

                     for (k = 0; k < ARRAY_SIZE(bclk_divs); ++k) {
                            if (!is_pll_freq_available(freq_in, freq_out))
                                   continue;

                            diff = sysclk - bclk * bclk_divs[k] / 10;
                            if (diff == 0) {
                                   *sysclk_idx = i;
                                   *dac_idx = j;
                                   *bclk_idx = k;
                                   best_freq_out = freq_out;
                                   break;
                            }
                            if (diff > 0 && closest > diff) {
                                   *sysclk_idx = i;
                                   *dac_idx = j;
                                   *bclk_idx = k;
                                   closest = diff;
                                   best_freq_out = freq_out;
                            }
                     }
                     if (k != ARRAY_SIZE(bclk_divs))
                            break;
              }
              if (j != ARRAY_SIZE(dac_divs))
                     break;
       }

       return best_freq_out;
}

In my opinion this is a compiler false positive. Any clue on how to rework this
would be welcomed :). I couldn't find any decent solution.

Daniel.