hwmon: (coretemp) Extend the bitmask to read temperature to 0xff

The Intel Software Development manual defines the temperature digital
readout as the bits [22:16] of the IA32_[PACKAGE]_THERM_STATUS registers.
Bit 23 is specified as reserved.

In recent processors, however, the temperature digital readout uses bits
[23:16]. In those processors, using the bitmask 0x7f would lead to
incorrect readings if the temperature deviates from TjMax by more than
127 degrees Celsius.

Although not guaranteed, bit 23 is likely to be 0 in processors from a few
generations ago. The temperature reading would still be correct in those
processors when using a 0xff bitmask.

Model-specific provisions can be made for older processors in which bit 23
is not 0 should the need arise.

Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Link: https://lore.kernel.org/r/20240425171311.19519-4-ricardo.neri-calderon@linux.intel.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/drivers/hwmon/coretemp.c b/drivers/hwmon/coretemp.c
index 616bd1a5b86419b5f710c1b4fceaaa584ad701d0..1b9203b20d7099d4782ebd5c75d9011be56fe330 100644 (file)
--- a/drivers/hwmon/coretemp.c
+++ b/drivers/hwmon/coretemp.c
@@ -411,7 +411,7 @@ static ssize_t show_temp(struct device *dev,
                 * Return it instead of reporting an error which doesn't
                 * really help at all.
                 */
-               tdata->temp = tjmax - ((eax >> 16) & 0x7f) * 1000;
+               tdata->temp = tjmax - ((eax >> 16) & 0xff) * 1000;
                tdata->last_updated = jiffies;
        }