Re: [linux-next:master 4727/8441] drivers/video/backlight/lp855x_bl.c:252:7: warning: variable 'ret' is used uninitialized whenever 'if' condition is false

[Lee Jones <lee@kernel.org>]

Arthur,

Please submit a follow-up patch or I'll have to revert it.

Thanks.

On Wed, 09 Aug 2023, kernel test robot wrote:

> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> head:   21ef7b1e17d039053edaeaf41142423810572741
> commit: 5145531be5fbad0e914d1dc1cbd392d7b756abaa [4727/8441] backlight: lp855x: Catch errors when changing brightness
> config: x86_64-buildonly-randconfig-r002-20230808 (https://download.01.org/0day-ci/archive/20230809/202308091728.NEJhgUPP-lkp@intel.com/config)
> compiler: clang version 16.0.4 (https://github.com/llvm/llvm-project.git ae42196bc493ffe877a7e3dff8be32035dea4d07)
> reproduce: (https://download.01.org/0day-ci/archive/20230809/202308091728.NEJhgUPP-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202308091728.NEJhgUPP-lkp@intel.com/
> 
> All warnings (new ones prefixed by >>):
> 
> >> drivers/video/backlight/lp855x_bl.c:252:7: warning: variable 'ret' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
>            else if (lp->mode == REGISTER_BASED)
>                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    include/linux/compiler.h:55:28: note: expanded from macro 'if'
>    #define if(cond, ...) if ( __trace_if_var( !!(cond , ## __VA_ARGS__) ) )
>                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    include/linux/compiler.h:57:30: note: expanded from macro '__trace_if_var'
>    #define __trace_if_var(cond) (__builtin_constant_p(cond) ? (cond) : __trace_if_value(cond))
>                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    drivers/video/backlight/lp855x_bl.c:256:9: note: uninitialized use occurs here
>            return ret;
>                   ^~~
>    drivers/video/backlight/lp855x_bl.c:252:7: note: remove the 'if' if its condition is always true
>            else if (lp->mode == REGISTER_BASED)
>                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    include/linux/compiler.h:55:23: note: expanded from macro 'if'
>    #define if(cond, ...) if ( __trace_if_var( !!(cond , ## __VA_ARGS__) ) )
>                          ^
>    drivers/video/backlight/lp855x_bl.c:244:9: note: initialize the variable 'ret' to silence this warning
>            int ret;
>                   ^
>                    = 0
>    1 warning generated.
> 
> 
> vim +252 drivers/video/backlight/lp855x_bl.c
> 
> 8cc9764c9c7d01 Kim, Milo    2012-12-17  239  
> 7be865ab8634d4 Kim, Milo    2012-03-23  240  static int lp855x_bl_update_status(struct backlight_device *bl)
> 7be865ab8634d4 Kim, Milo    2012-03-23  241  {
> 7be865ab8634d4 Kim, Milo    2012-03-23  242  	struct lp855x *lp = bl_get_data(bl);
> 61c1c6147f69d8 Sean Paul    2015-05-11  243  	int brightness = bl->props.brightness;
> 5145531be5fbad Artur Weber  2023-07-14  244  	int ret;
> 7be865ab8634d4 Kim, Milo    2012-03-23  245  
> 9f0a511f4a227c Shingo Nakao 2013-07-02  246  	if (bl->props.state & (BL_CORE_SUSPENDED | BL_CORE_FBBLANK))
> 61c1c6147f69d8 Sean Paul    2015-05-11  247  		brightness = 0;
> 7be865ab8634d4 Kim, Milo    2012-03-23  248  
> 61c1c6147f69d8 Sean Paul    2015-05-11  249  	if (lp->mode == PWM_BASED)
> 5145531be5fbad Artur Weber  2023-07-14  250  		ret = lp855x_pwm_ctrl(lp, brightness,
> 5145531be5fbad Artur Weber  2023-07-14  251  				      bl->props.max_brightness);
> 61c1c6147f69d8 Sean Paul    2015-05-11 @252  	else if (lp->mode == REGISTER_BASED)
> 5145531be5fbad Artur Weber  2023-07-14  253  		ret = lp855x_write_byte(lp, lp->cfg->reg_brightness,
> 5145531be5fbad Artur Weber  2023-07-14  254  					(u8)brightness);
> 7be865ab8634d4 Kim, Milo    2012-03-23  255  
> 5145531be5fbad Artur Weber  2023-07-14  256  	return ret;
> 7be865ab8634d4 Kim, Milo    2012-03-23  257  }
> 7be865ab8634d4 Kim, Milo    2012-03-23  258  
> 
> :::::: The code at line 252 was first introduced by commit
> :::::: 61c1c6147f69d8dea31fd133d2ec0b1594c9a3eb backlight: lp855x: Don't clear level on suspend/blank
> 
> :::::: TO: Sean Paul <seanpaul@chromium.org>
> :::::: CC: Lee Jones <lee.jones@linaro.org>
> 
> -- 
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki

-- 
Lee Jones [李琼斯]