hwmon: (jc42) do not allow writing to locked registers

On systems where the temperature sensor is actually used, the BIOS is
likely to have locked the alarm registers.  In that case, all writes
through the corresponding sysfs files would be silently ignored.

To prevent this, detect the locks and make the affected sysfs files
read-only.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Cc: stable@kernel.org
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>

1 files changed, 8 insertions, 4 deletions

diff --git a/Documentation/hwmon/jc42 b/Documentation/hwmon/jc42
index 2a0924003f92..a22ecf48f255 100644
--- a/Documentation/hwmon/jc42
+++ b/Documentation/hwmon/jc42
@@ -86,15 +86,19 @@ limits. The chip supports only a single register to configure the hysteresis,
 which applies to all limits. This register can be written by writing into
 temp1_crit_hyst. Other hysteresis attributes are read-only.
 
+If the BIOS has configured the sensor for automatic temperature management, it
+is likely that it has locked the registers, i.e., that the temperature limits
+cannot be changed.
+
 Sysfs entries
 -------------
 
 temp1_input             Temperature (RO)
-temp1_min               Minimum temperature (RW)
-temp1_max               Maximum temperature (RW)
-temp1_crit              Critical high temperature (RW)
+temp1_min               Minimum temperature (RO or RW)
+temp1_max               Maximum temperature (RO or RW)
+temp1_crit              Critical high temperature (RO or RW)
 
-temp1_crit_hyst         Critical hysteresis temperature (RW)
+temp1_crit_hyst         Critical hysteresis temperature (RO or RW)
 temp1_max_hyst          Maximum hysteresis temperature (RO)
 
 temp1_min_alarm         Temperature low alarm