Re: [PATCH] drm/bridge: lt9611uxc: support displays with up to 4 EDID blocks

[kernel test robot <lkp@intel.com>]

Hi,

kernel test robot noticed the following build warnings:

[auto build test WARNING on 4c26e162947f91aa78ba57dd4fddd38fc80e7d60]

url:    https://github.com/intel-lab-lkp/linux/commits/vishnu-saini-oss-qualcomm-com/drm-bridge-lt9611uxc-support-displays-with-up-to-4-EDID-blocks/20260518-021632
base:   4c26e162947f91aa78ba57dd4fddd38fc80e7d60
patch link:    https://lore.kernel.org/r/20260517-lt9611usc_edid34_misc_next-v1-1-5e2fd8c6399b%40oss.qualcomm.com
patch subject: [PATCH] drm/bridge: lt9611uxc: support displays with up to 4 EDID blocks
config: csky-randconfig-001-20260518 (https://download.01.org/0day-ci/archive/20260518/202605180850.uN2x73KR-lkp@intel.com/config)
compiler: csky-linux-gcc (GCC) 15.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260518/202605180850.uN2x73KR-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/202605180850.uN2x73KR-lkp@intel.com/

All warnings (new ones prefixed by >>):

   drivers/gpu/drm/bridge/lontium-lt9611uxc.c: In function 'lt9611uxc_get_edid_block':
>> drivers/gpu/drm/bridge/lontium-lt9611uxc.c:454:37: warning: 'memcmp' specified bound 8 exceeds source size 4 [-Wstringop-overread]
     454 |                 while (!ret && 0 == memcmp(&edid_header, &buf, 8) && retry_cnt-- > 0) {
         |                                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   drivers/gpu/drm/bridge/lontium-lt9611uxc.c:415:53: note: source object allocated here
     415 | static int lt9611uxc_get_edid_block(void *data, u8 *buf, unsigned int block, size_t len)
         |                                                 ~~~~^~~


vim +/memcmp +454 drivers/gpu/drm/bridge/lontium-lt9611uxc.c

   414	
   415	static int lt9611uxc_get_edid_block(void *data, u8 *buf, unsigned int block, size_t len)
   416	{
   417		struct lt9611uxc *lt9611uxc = data;
   418		int ret = 0;
   419		int retry_cnt = 10;
   420		int edid_ext_block;
   421		const u8 edid_header[8] = { 0x00, 0xFF, 0xFF, 0xFF,
   422					    0xFF, 0xFF, 0xFF, 0x00 };
   423	
   424		if (len > EDID_BLOCK_SIZE)
   425			return -EINVAL;
   426	
   427		if (block >= EDID_NUM_BLOCKS)
   428			return -EINVAL;
   429	
   430		if (block == 2) {
   431			lt9611uxc_lock(lt9611uxc);
   432	
   433			/* Read number of block available in EDID data */
   434			ret = regmap_read(lt9611uxc->regmap, 0xb02a, &edid_ext_block);
   435			if (ret) {
   436				dev_err(lt9611uxc->dev, "edid block read failed: %d\n", ret);
   437				lt9611uxc_unlock(lt9611uxc);
   438				return ret;
   439			}
   440	
   441			/* Reset EDID ready flag so that lt9611uxc can read 2nd and 3rd block */
   442			regmap_write(lt9611uxc->regmap, 0xb02a, (edid_ext_block & (~BIT(3))));
   443	
   444			lt9611uxc_unlock(lt9611uxc);
   445	
   446			msleep(100);
   447	
   448			ret = lt9611uxc_read_edid_block(lt9611uxc, block, buf, len);
   449	
   450			/*
   451			 * Compare first 8 bytes of EDID header (0th block) and 2nd block to confirm
   452			 * that 2nd EDID block data is read successfully by lt9611uxc
   453			 */
 > 454			while (!ret && 0 == memcmp(&edid_header, &buf, 8) && retry_cnt-- > 0) {
   455				msleep(100);
   456				ret = lt9611uxc_read_edid_block(lt9611uxc, block, buf, len);
   457			}
   458		} else {
   459			ret = lt9611uxc_read_edid_block(lt9611uxc, block, buf, len);
   460		}
   461	
   462		return ret;
   463	};
   464	

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