linux-kernel - drivers/gpu/drm/stm/ltdc.c:1124 ltdc_crtc_set_crc_source() warn: variable dereferenced before check 'crtc' (see line 1119)

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Date:   Sat, 24 Dec 2022 14:04:20 +0300
From:   Dan Carpenter <error27@...il.com>
To:     oe-kbuild@...ts.linux.dev,
        Raphael Gallais-Pou <raphael.gallais-pou@...s.st.com>
Cc:     lkp@...el.com, oe-kbuild-all@...ts.linux.dev,
        linux-kernel@...r.kernel.org,
        Philippe Cornu <philippe.cornu@...s.st.com>
Subject: drivers/gpu/drm/stm/ltdc.c:1124 ltdc_crtc_set_crc_source() warn:
 variable dereferenced before check 'crtc' (see line 1119)

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   72a85e2b0a1e1e6fb4ee51ae902730212b2de25c
commit: 79b44684a14e363d24c299b772f037344ad8c8dc drm/stm: ltdc: add support for CRC hashing feature
config: arm-randconfig-m041-20221224
compiler: arm-linux-gnueabi-gcc (GCC) 12.1.0

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@...el.com>
| Reported-by: Dan Carpenter <error27@...il.com>

New smatch warnings:
drivers/gpu/drm/stm/ltdc.c:1124 ltdc_crtc_set_crc_source() warn: variable dereferenced before check 'crtc' (see line 1119)

Old smatch warnings:
drivers/gpu/drm/stm/ltdc.c:901 ltdc_crtc_mode_set_nofb() warn: iterator used outside loop: 'bridge'
drivers/gpu/drm/stm/ltdc.c:911 ltdc_crtc_mode_set_nofb() warn: pm_runtime_get_sync() also returns 1 on success

vim +/crtc +1124 drivers/gpu/drm/stm/ltdc.c

79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1117  static int ltdc_crtc_set_crc_source(struct drm_crtc *crtc, const char *source)
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1118  {
79b44684a14e36 Raphael Gallais-Pou 2022-02-11 @1119  	struct ltdc_device *ldev = crtc_to_ltdc(crtc);
                                                                                                ^^^^
Derefernce

79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1120  	int ret;
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1121  
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1122  	DRM_DEBUG_DRIVER("\n");
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1123  
79b44684a14e36 Raphael Gallais-Pou 2022-02-11 @1124  	if (!crtc)
                                                            ^^^^^
Checked too late.

79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1125  		return -ENODEV;
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1126  
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1127  	if (source && strcmp(source, "auto") == 0) {
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1128  		ldev->crc_active = true;
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1129  		ret = regmap_set_bits(ldev->regmap, LTDC_GCR, GCR_CRCEN);
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1130  	} else if (!source) {
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1131  		ldev->crc_active = false;
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1132  		ret = regmap_clear_bits(ldev->regmap, LTDC_GCR, GCR_CRCEN);
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1133  	} else {
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1134  		ret = -EINVAL;
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1135  	}
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1136  
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1137  	ldev->crc_skip_count = 0;
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1138  	return ret;
79b44684a14e36 Raphael Gallais-Pou 2022-02-11  1139  }

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