Re: [PATCH] drm/stm: ltdc: unify log system

Hi Raphael,

kernel test robot noticed the following build warnings:

https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Raphael-Gallais-Pou/drm-stm-ltdc-unify-log-system/20250821-210930
base:   https://git.kernel.org/pub/scm/linux/kernel/git/atorgue/stm32.git stm32-next
patch link:    https://lore.kernel.org/r/20250821130356.883553-1-raphael.gallais-pou%40foss.st.com
patch subject: [PATCH] drm/stm: ltdc: unify log system
config: arm-randconfig-r072-20250824 (https://download.01.org/0day-ci/archive/20250825/202508250637.nLxtkS26-lkp@intel.com/config)
compiler: arm-linux-gnueabi-gcc (GCC) 8.5.0

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 [off-list ref]
| Reported-by: Dan Carpenter [off-list ref]
| Closes: https://lore.kernel.org/r/202508250637.nLxtkS26-lkp@intel.com/ (local)

New smatch warnings:
drivers/gpu/drm/stm/ltdc.c:1150 ltdc_crtc_set_crc_source() warn: variable dereferenced before check 'crtc' (see line 1148)
drivers/gpu/drm/stm/ltdc.c:1174 ltdc_crtc_verify_crc_source() warn: variable dereferenced before check 'crtc' (see line 1172)

vim +/crtc +1150 drivers/gpu/drm/stm/ltdc.c

79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1143  static int ltdc_crtc_set_crc_source(struct drm_crtc *crtc, const char *source)
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1144  {
898a9e3f56db98 Raphael Gallais-Pou 2023-05-15  1145  	struct ltdc_device *ldev;
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1146  	int ret;
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1147  
fa2b2390600532 Raphael Gallais-Pou 2025-08-21 @1148  	drm_dbg_driver(crtc->dev, "\n");
                                                                       ^^^^^^^^^
Dereference.  A lot of the time people would suggest to delete these
types of printks and use ftrace instead.

79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1149  
79b44684a14e36 Raphael Gallais-Pou 2022-02-11 @1150  	if (!crtc)
                                                            ^^^^^
Checked too late.

79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1151  		return -ENODEV;
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1152  
898a9e3f56db98 Raphael Gallais-Pou 2023-05-15  1153  	ldev = crtc_to_ltdc(crtc);
898a9e3f56db98 Raphael Gallais-Pou 2023-05-15  1154  
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1155  	if (source && strcmp(source, "auto") == 0) {
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1156  		ldev->crc_active = true;
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1157  		ret = regmap_set_bits(ldev->regmap, LTDC_GCR, GCR_CRCEN);
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1158  	} else if (!source) {
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1159  		ldev->crc_active = false;
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1160  		ret = regmap_clear_bits(ldev->regmap, LTDC_GCR, GCR_CRCEN);
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1161  	} else {
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1162  		ret = -EINVAL;
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1163  	}
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1164  
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1165  	ldev->crc_skip_count = 0;
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1166  	return ret;
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1167  }
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1168  
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1169  static int ltdc_crtc_verify_crc_source(struct drm_crtc *crtc,
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1170  				       const char *source, size_t *values_cnt)
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1171  {
fa2b2390600532 Raphael Gallais-Pou 2025-08-21 @1172  	drm_dbg_driver(crtc->dev, "\n");
                                                                        ^^^^^^^^
Dereference

79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1173  
79b44684a14e36 Raphael Gallais-Pou 2022-02-11 @1174  	if (!crtc)
                                                            ^^^^^
Too late.

79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1175  		return -ENODEV;
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1176  
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1177  	if (source && strcmp(source, "auto") != 0) {
fa2b2390600532 Raphael Gallais-Pou 2025-08-21  1178  		drm_dbg_driver(crtc->dev, "Unknown CRC source %s for %s\n",
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1179  			       source, crtc->name);
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1180  		return -EINVAL;
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1181  	}
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1182  
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1183  	*values_cnt = 1;
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1184  	return 0;
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1185  }

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki