hwmon: (coretemp) Let the user force TjMax

On old CPUs (and even some recent Atom CPUs) TjMax can't be read from
the CPU registers, so it is guessed by the driver using a complex
heuristic which isn't reliable. So let users who know their CPU's
TjMax pass it as a module parameter.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: "R, Durgadoss" <durgadoss.r@intel.com>
Cc: Guenter Roeck <guenter.roeck@ericsson.com>
Cc: Alexander Stein <alexander.stein@systec-electronic.com>
Acked-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>

2 files changed, 19 insertions, 3 deletions

diff --git a/Documentation/hwmon/coretemp b/Documentation/hwmon/coretemp
index fa8776ab9b18..49c0d42dde86 100644
--- a/Documentation/hwmon/coretemp
+++ b/Documentation/hwmon/coretemp
@@ -49,9 +49,10 @@ tempX_label	 - Contains string "Core X", where X is processor
                    number. For Package temp, this will be "Physical id Y",
                    where Y is the package number.
 
-The TjMax temperature is set to 85 degrees C if undocumented model specific
-register (UMSR) 0xee has bit 30 set. If not the TjMax is 100 degrees C as
-(sometimes) documented in processor datasheet.
+On CPU models which support it, TjMax is read from a model-specific register.
+On other models, it is set to an arbitrary value based on weak heuristics.
+If these heuristics don't work for you, you can pass the correct TjMax value
+as a module parameter (tjmax).
 
 Appendix A. Known TjMax lists (TBD):
 Some information comes from ark.intel.com
diff --git a/drivers/hwmon/coretemp.c b/drivers/hwmon/coretemp.c
index 256f70803eb3..5a41e9dda909 100644
--- a/drivers/hwmon/coretemp.c
+++ b/drivers/hwmon/coretemp.c
@@ -36,11 +36,20 @@
 #include <linux/cpu.h>
 #include <linux/pci.h>
 #include <linux/smp.h>
+#include <linux/moduleparam.h>
 #include <asm/msr.h>
 #include <asm/processor.h>
 
 #define DRVNAME "coretemp"
 
+/*
+ * force_tjmax only matters when TjMax can't be read from the CPU itself.
+ * When set, it replaces the driver's suboptimal heuristic.
+ */
+static int force_tjmax;
+module_param_named(tjmax, force_tjmax, int, 0444);
+MODULE_PARM_DESC(tjmax, "TjMax value in degrees Celsius");
+
 #define BASE_SYSFS_ATTR_NO      2       /* Sysfs Base attr no for coretemp */
 #define NUM_REAL_CORES          16      /* Number of Real cores per cpu */
 #define CORETEMP_NAME_LENGTH    17      /* String Length of attrs */
@@ -398,6 +407,12 @@ static int get_tjmax(struct cpuinfo_x86 *c, u32 id, struct device *dev)
                 }
         }
 
+        if (force_tjmax) {
+                dev_notice(dev, "TjMax forced to %d degrees C by user\n",
+                           force_tjmax);
+                return force_tjmax * 1000;
+        }
+
         /*
          * An assumption is made for early CPUs and unreadable MSR.
          * NOTE: the calculated value may not be correct.