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Date: Mon, 24 Apr 2017 17:27:25 +0200
From: Arnd Bergmann <arnd@...db.de>
To: Daniel Baluta <daniel.baluta@...il.com>
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 Mon, Apr 24, 2017 at 3:15 PM, Daniel Baluta <daniel.baluta@...il.com> wrote:
> 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.
Actually I think in this case the compiler is supposed to warn if
best_freq_out is not initialized, as we would never set it
in case is_pll_freq_available() returns false for all inputs or
sysclk_divs[] is -1 for all fields.
I'd leave the initialization then, and only replace the breaks
with a goto (not tested):
> » 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;
> » » » » » goto out;
> » » » » }
> » » » » if (diff > 0 && closest > diff) {
> » » » » » *sysclk_idx = i;
> » » » » » *dac_idx = j;
> » » » » » *bclk_idx = k;
> » » » » » closest = diff;
> » » » » » best_freq_out = freq_out;
> » » » » }
> » » » }
> » » }
> » }
>out:
> » return best_freq_out;
> }
Arnd
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