thermal: rockchip: make temperature reporting much more accurate

In general, the kernel should report temperature readings exactly as
reported by the hardware. The cpu / gpu thermal driver works in 5 degree
increments,but we ought to do more accurate. The temperature will do
linear interpolation between the entries in the table.

Test= $md5sum /dev/zero &
$while true; do grep "" /sys/class/thermal/thermal_zone[1-2]/temp;
sleep .5; done

e.g. We can get the result as follows:
    /sys/class/thermal/thermal_zone1/temp:39994
    /sys/class/thermal/thermal_zone2/temp:39086
    /sys/class/thermal/thermal_zone1/temp:39994
    /sys/class/thermal/thermal_zone2/temp:39540
    /sys/class/thermal/thermal_zone1/temp:39540
    /sys/class/thermal/thermal_zone2/temp:39540
    /sys/class/thermal/thermal_zone1/temp:39540
    /sys/class/thermal/thermal_zone2/temp:39994

Reviewed-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Reviewed-by: Daniel Kurtz <djkurtz@chromium.org>
Signed-off-by: Caesar Wang <wxt@rock-chips.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>

diff --git a/drivers/thermal/rockchip_thermal.c b/drivers/thermal/rockchip_thermal.c
index 9c6ce548e36312f95ca49f6352cf4999a1ab0fe0..3aa46ac7cdbc33765a90279da09fd84507a09d6c 100644 (file)
--- a/drivers/thermal/rockchip_thermal.c
+++ b/drivers/thermal/rockchip_thermal.c
@@ -193,19 +193,20 @@ static u32 rk_tsadcv2_temp_to_code(long temp)
 
 static long rk_tsadcv2_code_to_temp(u32 code)
 {
-       int high, low, mid;
-
-       low = 0;
-       high = ARRAY_SIZE(v2_code_table) - 1;
-       mid = (high + low) / 2;
-
-       if (code > v2_code_table[low].code || code < v2_code_table[high].code)
-               return 125000; /* No code available, return max temperature */
+       unsigned int low = 0;
+       unsigned int high = ARRAY_SIZE(v2_code_table) - 1;
+       unsigned int mid = (low + high) / 2;
+       unsigned int num;
+       unsigned long denom;
+
+       /* Invalid code, return -EAGAIN */
+       if (code > TSADCV2_DATA_MASK)
+               return -EAGAIN;
 
-       while (low <= high) {
-               if (code >= v2_code_table[mid].code && code <
-                   v2_code_table[mid - 1].code)
-                       return v2_code_table[mid].temp;
+       while (low <= high && mid) {
+               if (code >= v2_code_table[mid].code &&
+                   code < v2_code_table[mid - 1].code)
+                       break;
                else if (code < v2_code_table[mid].code)
                        low = mid + 1;
                else
@@ -213,7 +214,16 @@ static long rk_tsadcv2_code_to_temp(u32 code)
                mid = (low + high) / 2;
        }
 
-       return 125000;
+       /*
+        * The 5C granularity provided by the table is too much. Let's
+        * assume that the relationship between sensor readings and
+        * temperature between 2 table entries is linear and interpolate
+        * to produce less granular result.
+        */
+       num = v2_code_table[mid].temp - v2_code_table[mid - 1].temp;
+       num *= v2_code_table[mid - 1].code - code;
+       denom = v2_code_table[mid - 1].code - v2_code_table[mid].code;
+       return v2_code_table[mid - 1].temp + (num / denom);
 }
 
 /**