linux-kernel - Re: [PATCH] ASoC: codes: src4xxx: Avoid clang -Wsometimes-uninitialized in src4xxx_hw

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Date:   Tue, 23 Aug 2022 08:35:26 +1000
From:   Matt Flax <flatmax@...tmax.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        patches@...ts.linux.dev, kernel test robot <lkp@...el.com>,
        "Sudip Mukherjee (Codethink)" <sudipm.mukherjee@...il.com>
Subject: Re: [PATCH] ASoC: codes: src4xxx: Avoid clang
 -Wsometimes-uninitialized in src4xxx_hw_params()

That solution looks good.

Matt

On 23/8/22 08:32, Nathan Chancellor wrote:
> Hi Matt,
>
> On Tue, Aug 23, 2022 at 08:00:07AM +1000, Matt Flax wrote:
>> Hi Nathan,
>>
>> On 23/8/22 04:31, Nathan Chancellor wrote:
>>> Clang warns:
>>>
>>>     sound/soc/codecs/src4xxx.c:280:3: error: variable 'd' is used uninitialized whenever switch default is taken [-Werror,-Wsometimes-uninitialized]
>>>                     default:
>>>                     ^~~~~~~
>>>     sound/soc/codecs/src4xxx.c:298:59: note: uninitialized use occurs here
>>>                     ret = regmap_write(src4xxx->regmap, SRC4XXX_RCV_PLL_11, d);
>>>                                                                             ^
>>>     sound/soc/codecs/src4xxx.c:223:20: note: initialize the variable 'd' to silence this warning
>>>             int val, pj, jd, d;
>>>                               ^
>>>                               = 0
>>
>> If you really want to get rid of these warnings, you can use this default
>> for the variables :
>>
>> pj = 0x0;
>> jd=0xff;
>>
>> d = 0xff;
>>
>> It doesn't really make sense why we would choose to initialise these
>> variables, but if you want to silence the preprocessor, then perhaps those
>> values. Put a message that defaults are not known nor specified in the data
>> sheet and these values are chosen to be unlikely matches of real world
>> values - which ensures regmap updates later from an initial unknown chip
>> state after refresh.
> Okay, I could do something like this?
>
> diff --git a/sound/soc/codecs/src4xxx.c b/sound/soc/codecs/src4xxx.c
> index a8f143057b41..db4e280dd055 100644
> --- a/sound/soc/codecs/src4xxx.c
> +++ b/sound/soc/codecs/src4xxx.c
> @@ -280,9 +280,14 @@ static int src4xxx_hw_params(struct snd_pcm_substream *substream,
>   		default:
>   			/* don't error out here,
>   			 * other parts of the chip are still functional
> +			 * Dummy initialize variables to avoid
> +			 * -Wsometimes-uninitialized from clang.
>   			 */
>   			dev_info(component->dev,
> -				"Couldn't set the RCV PLL as this master clock rate is unknown\n");
> +				"Couldn't set the RCV PLL as this master clock rate is unknown. Chosen regmap values may not match real world values.\n");
> +			pj = 0x0;
> +			jd = 0xff;
> +			d = 0xff;
>   			break;
>   		}
>   		ret = regmap_write(src4xxx->regmap, SRC4XXX_RCV_PLL_0F, pj);
>
> These warnings need to be eliminated because Linus requires a clean
> build as much as possible [1] [2], which has been codified by
> CONFIG_WERROR, which is enabled by default with allmodconfig. As a
> result, clang allmodconfig builds are broken [3], which you might have
> already seen. If there is another way this could be written without
> potentially uninitialized variables, I am open to it.
>
> [1]: https://lore.kernel.org/CAHk-=wg-mH-_GYpkhz_psjBWG6ZcjKnPo83fg7YMj_by+-LRTQ@mail.gmail.com/
> [2]: https://lore.kernel.org/CAHk-=wi4wyvuXs0SUq-2x=XHxWmJ6jVKRD-WpE0kWgWiqVJNbg@mail.gmail.com/
> [3]: https://lore.kernel.org/YwNMUlAmu%2FqCjuva@debian/
>
>> All a bit messy really.
> Indeed :/
>
>>> According to the comment in the default case, other parts of the chip
>>> are still functional without these values so just return 0 in the
>>> default case to avoid using these variables uninitialized.
>>>
>>> Link: https://github.com/ClangBuiltLinux/linux/issues/1691
>>> Reported-by: kernel test robot <lkp@...el.com>
>>> Reported-by: "Sudip Mukherjee (Codethink)" <sudipm.mukherjee@...il.com>
>>> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
>>> ---
>>>    sound/soc/codecs/src4xxx.c | 2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/sound/soc/codecs/src4xxx.c b/sound/soc/codecs/src4xxx.c
>>> index a8f143057b41..cf45caa4bf7f 100644
>>> --- a/sound/soc/codecs/src4xxx.c
>>> +++ b/sound/soc/codecs/src4xxx.c
>>> @@ -283,7 +283,7 @@ static int src4xxx_hw_params(struct snd_pcm_substream *substream,
>>>    			 */
>>>    			dev_info(component->dev,
>>>    				"Couldn't set the RCV PLL as this master clock rate is unknown\n");
>>> -			break;
>>> +			return 0;
>>
>> Don't return here, the rest of the chip is still functional and probably in
>> use. Print the dev_info and continue.
> I'll send a v2 tomorrow morning (for me at least) if there are no other
> comments.
>
> Cheers,
> Nathan