[linux-next:master 16319/17742] drivers/gpu/drm/xe/xe_hwmon.c:1344 xe_hwmon_temperature_decode() warn: impossible condition '(value > ((~0 >> 1))) => (s64min-s64max > s64max)'

[linux-next:master 16319/17742] drivers/gpu/drm/xe/xe_hwmon.c:1344 xe_hwmon_temperature_decode() warn: impossible condition '(value > ((~0 >> 1))) => (s64min-s64max > s64max)'

[kernel test robot]

Unfiltered warning: this smatch report is sent as-is and has not been
reviewed for false positives, so please treat it with due skepticism.

BCC: lkp@intel.com
CC: oe-kbuild-all@lists.linux.dev
TO: Karthik Poosa <karthik.poosa@intel.com>
CC: Rodrigo Vivi <rodrigo.vivi@intel.com>

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
head:   3d229ce89862b8e82d71a9e11d6f840ca272a6d6
commit: 24ec15d646179a255f314e404343bf8e3200c9c0 [16319/17742] drm/xe/hwmon: Decode CRI temperature registers as IEEE-754
:::::: branch date: 14 hours ago
:::::: commit date: 5 days ago
config: x86_64-randconfig-r2202-20261019 (https://download.01.org/0day-ci/archive/20261020/202610200910.SP0zWbkd-lkp@intel.com/config)
compiler: clang version 22.1.8 (https://github.com/llvm/llvm-project ca7933e47d3a3451d81e72ac174dcb5aa28b59d1)
rustc: rustc 1.96.0 (ac68faa20 2026-05-25)
smatch: v0.5.0-9187-g5189e3fb

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>
| Reported-by: Dan Carpenter <error27@gmail.com>
| Closes: https://lore.kernel.org/r/202610200910.SP0zWbkd-lkp@intel.com/

smatch warnings:
drivers/gpu/drm/xe/xe_hwmon.c:1344 xe_hwmon_temperature_decode() warn: impossible condition '(value > ((~0 >> 1))) => (s64min-s64max > s64max)'

vim +1344 drivers/gpu/drm/xe/xe_hwmon.c

24ec15d646179a Karthik Poosa 2026-10-15  1296  
24ec15d646179a Karthik Poosa 2026-10-15  1297  /**
24ec15d646179a Karthik Poosa 2026-10-15  1298   * xe_hwmon_temperature_decode - Decode an IEEE-754 temperature register value
24ec15d646179a Karthik Poosa 2026-10-15  1299   * @reg_val: The raw register value to decode
24ec15d646179a Karthik Poosa 2026-10-15  1300   * @temperature: Pointer to store the decoded temperature in millidegrees Celsius.
24ec15d646179a Karthik Poosa 2026-10-15  1301   *
24ec15d646179a Karthik Poosa 2026-10-15  1302   * IEEE-754 single-precision format:
24ec15d646179a Karthik Poosa 2026-10-15  1303   *
24ec15d646179a Karthik Poosa 2026-10-15  1304   *  31 30                         23 22                         0
24ec15d646179a Karthik Poosa 2026-10-15  1305   * +--+-----------------------------+----------------------------+
24ec15d646179a Karthik Poosa 2026-10-15  1306   * | S|          exponent           |          fraction          |
24ec15d646179a Karthik Poosa 2026-10-15  1307   * +--+-----------------------------+----------------------------+
24ec15d646179a Karthik Poosa 2026-10-15  1308   *
24ec15d646179a Karthik Poosa 2026-10-15  1309   * value = (-1)^S * 1.fraction * 2^(exponent - 127)
24ec15d646179a Karthik Poosa 2026-10-15  1310   *
24ec15d646179a Karthik Poosa 2026-10-15  1311   * Return: 0 on success or an error if @reg_val is non-finite or cannot be
24ec15d646179a Karthik Poosa 2026-10-15  1312   * represented in millidegrees Celsius.
24ec15d646179a Karthik Poosa 2026-10-15  1313   */
24ec15d646179a Karthik Poosa 2026-10-15  1314  static int xe_hwmon_temperature_decode(u32 reg_val, long *temperature)
24ec15d646179a Karthik Poosa 2026-10-15  1315  {
24ec15d646179a Karthik Poosa 2026-10-15  1316  	u32 exponent = REG_FIELD_GET(IEEE754_EXP_MASK, reg_val);
24ec15d646179a Karthik Poosa 2026-10-15  1317  	u32 mantissa = REG_FIELD_GET(IEEE754_MANTISSA_MASK, reg_val);
24ec15d646179a Karthik Poosa 2026-10-15  1318  	s64 value;
24ec15d646179a Karthik Poosa 2026-10-15  1319  	int shift;
24ec15d646179a Karthik Poosa 2026-10-15  1320  
24ec15d646179a Karthik Poosa 2026-10-15  1321  	/* Exponent 0xff encodes infinity or NaN. */
24ec15d646179a Karthik Poosa 2026-10-15  1322  	if (exponent == IEEE754_EXP_SPECIAL)
24ec15d646179a Karthik Poosa 2026-10-15  1323  		return -EINVAL;
24ec15d646179a Karthik Poosa 2026-10-15  1324  
24ec15d646179a Karthik Poosa 2026-10-15  1325  	/* Subnormal values are smaller than one millidegree Celsius. */
24ec15d646179a Karthik Poosa 2026-10-15  1326  	if (!exponent) {
24ec15d646179a Karthik Poosa 2026-10-15  1327  		*temperature = 0;
24ec15d646179a Karthik Poosa 2026-10-15  1328  		return 0;
24ec15d646179a Karthik Poosa 2026-10-15  1329  	}
24ec15d646179a Karthik Poosa 2026-10-15  1330  
24ec15d646179a Karthik Poosa 2026-10-15  1331  	value = (s64)(mantissa | BIT(IEEE754_MANTISSA_BITS)) * MILLIDEGREE_PER_DEGREE;
24ec15d646179a Karthik Poosa 2026-10-15  1332  	shift = exponent - (IEEE754_EXP_BIAS + IEEE754_MANTISSA_BITS);
24ec15d646179a Karthik Poosa 2026-10-15  1333  	if (shift >= 0) {
24ec15d646179a Karthik Poosa 2026-10-15  1334  		if (shift >= BITS_PER_LONG || value > (LONG_MAX >> shift))
24ec15d646179a Karthik Poosa 2026-10-15  1335  			return -ERANGE;
24ec15d646179a Karthik Poosa 2026-10-15  1336  		value <<= shift;
24ec15d646179a Karthik Poosa 2026-10-15  1337  	} else if (shift > -64) {
24ec15d646179a Karthik Poosa 2026-10-15  1338  		value >>= -shift;
24ec15d646179a Karthik Poosa 2026-10-15  1339  	} else {
24ec15d646179a Karthik Poosa 2026-10-15  1340  		value = 0;
24ec15d646179a Karthik Poosa 2026-10-15  1341  	}
24ec15d646179a Karthik Poosa 2026-10-15  1342  
24ec15d646179a Karthik Poosa 2026-10-15  1343  	/* Ensure the magnitude fits in long, which is 32-bit on some arches. */
24ec15d646179a Karthik Poosa 2026-10-15 @1344  	if (value > LONG_MAX)
24ec15d646179a Karthik Poosa 2026-10-15  1345  		return -ERANGE;
24ec15d646179a Karthik Poosa 2026-10-15  1346  
24ec15d646179a Karthik Poosa 2026-10-15  1347  	if (reg_val & IEEE754_SIGN)
24ec15d646179a Karthik Poosa 2026-10-15  1348  		value = -value;
24ec15d646179a Karthik Poosa 2026-10-15  1349  
24ec15d646179a Karthik Poosa 2026-10-15  1350  	*temperature = value;
24ec15d646179a Karthik Poosa 2026-10-15  1351  	return 0;
24ec15d646179a Karthik Poosa 2026-10-15  1352  }
24ec15d646179a Karthik Poosa 2026-10-15  1353  

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