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

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Date:   Mon, 24 Apr 2017 16:15:33 +0300
From:   Daniel Baluta <daniel.baluta@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Daniel Baluta <daniel.baluta@....com>, alsa-devel@...a-project.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        patches@...nsource.wolfsonmicro.com, Takashi Iwai <tiwai@...e.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>
Subject: Re: [alsa-devel] [PATCH 1/2] ASoC: codec: wm9860: avoid
 maybe-uninitialized warning

On Fri, Apr 21, 2017 at 5:46 PM, Arnd Bergmann <arnd@...db.de> wrote:
> On Fri, Apr 21, 2017 at 3:07 PM, Daniel Baluta <daniel.baluta@....com> 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@...db.de>
>> Signed-off-by: Daniel Baluta <daniel.baluta@....com>
>> ---
>> 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.