[PATCH] drm/amd/display: restore edid reading from a given i2c adapter

[Dan Carpenter]

Hi Melissa,

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/Melissa-Wen/drm-amd-display-restore-edid-reading-from-a-given-i2c-adapter/20250210-070016
base:   https://git.kernel.org/pub/scm/linux/kernel/git/daeinki/drm-exynos.git exynos-drm-next
patch link:    https://lore.kernel.org/r/20250209225843.7412-1-mwen%40igalia.com
patch subject: [PATCH] drm/amd/display: restore edid reading from a given i2c adapter
config: x86_64-randconfig-161-20250211 (https://download.01.org/0day-ci/archive/20250212/202502121000.EBCEdoo9-lkp@intel.com/config)
compiler: clang version 19.1.3 (https://github.com/llvm/llvm-project ab51eccf88f5321e7c60591c5546b254b6afab99)

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 at intel.com>
| Reported-by: Dan Carpenter <dan.carpenter at linaro.org>
| Closes: https://lore.kernel.org/r/202502121000.EBCEdoo9-lkp@intel.com/

New smatch warnings:
drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c:7201 amdgpu_dm_connector_funcs_force() warn: variable dereferenced before check 'dc_link' (see line 7187)

Old smatch warnings:
drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c:12110 parse_edid_displayid_vrr() warn: variable dereferenced before check 'edid_ext' (see line 12106)

vim +/dc_link +7201 drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c

dae343b343ff741 Arnd Bergmann 2023-05-01  7179  static void amdgpu_dm_connector_funcs_force(struct drm_connector *connector)
0ba4a784a14592a Alex Hung     2023-04-05  7180  {
0ba4a784a14592a Alex Hung     2023-04-05  7181  	struct amdgpu_dm_connector *aconnector = to_amdgpu_dm_connector(connector);
0ba4a784a14592a Alex Hung     2023-04-05  7182  	struct dc_link *dc_link = aconnector->dc_link;
0ba4a784a14592a Alex Hung     2023-04-05  7183  	struct dc_sink *dc_em_sink = aconnector->dc_em_sink;
48edb2a4256eedf Melissa Wen   2024-09-27  7184  	const struct drm_edid *drm_edid;
be1aae525741575 Melissa Wen   2025-02-09  7185  	struct i2c_adapter *ddc;
0ba4a784a14592a Alex Hung     2023-04-05  7186  
be1aae525741575 Melissa Wen   2025-02-09 @7187  	if (dc_link->aux_mode)
                                                            ^^^^^^^^^^^^^^^^^
Unchecked dereference

be1aae525741575 Melissa Wen   2025-02-09  7188  		ddc = &aconnector->dm_dp_aux.aux.ddc;
be1aae525741575 Melissa Wen   2025-02-09  7189  	else
be1aae525741575 Melissa Wen   2025-02-09  7190  		ddc = &aconnector->i2c->base;
be1aae525741575 Melissa Wen   2025-02-09  7191  
be1aae525741575 Melissa Wen   2025-02-09  7192  	drm_edid = drm_edid_read_ddc(connector, ddc);
48edb2a4256eedf Melissa Wen   2024-09-27  7193  	drm_edid_connector_update(connector, drm_edid);
48edb2a4256eedf Melissa Wen   2024-09-27  7194  	if (!drm_edid) {
0e859faf8670a78 Alex Hung     2023-08-25  7195  		DRM_ERROR("No EDID found on connector: %s.\n", connector->name);
0ba4a784a14592a Alex Hung     2023-04-05  7196  		return;
0e859faf8670a78 Alex Hung     2023-08-25  7197  	}
0ba4a784a14592a Alex Hung     2023-04-05  7198  
48edb2a4256eedf Melissa Wen   2024-09-27  7199  	aconnector->drm_edid = drm_edid;
0ba4a784a14592a Alex Hung     2023-04-05  7200  	/* Update emulated (virtual) sink's EDID */
0ba4a784a14592a Alex Hung     2023-04-05 @7201  	if (dc_em_sink && dc_link) {
                                                                          ^^^^^^^
This code assumes dc_link can be NULL

48edb2a4256eedf Melissa Wen   2024-09-27  7202  		// FIXME: Get rid of drm_edid_raw()
48edb2a4256eedf Melissa Wen   2024-09-27  7203  		const struct edid *edid = drm_edid_raw(drm_edid);
48edb2a4256eedf Melissa Wen   2024-09-27  7204  
0ba4a784a14592a Alex Hung     2023-04-05  7205  		memset(&dc_em_sink->edid_caps, 0, sizeof(struct dc_edid_caps));
48edb2a4256eedf Melissa Wen   2024-09-27  7206  		memmove(dc_em_sink->dc_edid.raw_edid, edid,
48edb2a4256eedf Melissa Wen   2024-09-27  7207  			(edid->extensions + 1) * EDID_LENGTH);
0ba4a784a14592a Alex Hung     2023-04-05  7208  		dm_helpers_parse_edid_caps(
0ba4a784a14592a Alex Hung     2023-04-05  7209  			dc_link,
0ba4a784a14592a Alex Hung     2023-04-05  7210  			&dc_em_sink->dc_edid,
0ba4a784a14592a Alex Hung     2023-04-05  7211  			&dc_em_sink->edid_caps);
0ba4a784a14592a Alex Hung     2023-04-05  7212  	}
0ba4a784a14592a Alex Hung     2023-04-05  7213  }

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