[PATCH v2] thermal: rockchip: make temperature reporting much more accurate

From: Caesar Wang
Date: Sun Jan 18 2015 - 18:56:32 EST


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

Signed-off-by: Caesar Wang <wxt@xxxxxxxxxxxxxx>
Reviewed-by: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>

---

Changes in v2:
Reviewed-by: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>

drivers/thermal/rockchip_thermal.c | 26 +++++++++++++++++---------
1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/drivers/thermal/rockchip_thermal.c b/drivers/thermal/rockchip_thermal.c
index 1bcddfc..a7ae23a 100644
--- a/drivers/thermal/rockchip_thermal.c
+++ b/drivers/thermal/rockchip_thermal.c
@@ -193,19 +193,18 @@ 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;
+ unsigned int low = 0;
+ unsigned int high = ARRAY_SIZE(v2_code_table) - 1;
+ unsigned int mid = (low + high) / 2;
+ unsigned int scale;

if (code > v2_code_table[low].code || code < v2_code_table[high].code)
return 125000; /* No code available, return max temperature */

while (low <= high) {
- if (code >= v2_code_table[mid].code && code <
- v2_code_table[mid - 1].code)
- return v2_code_table[mid].temp;
+ 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 +212,16 @@ 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 extrapolate
+ * to produce less granular result.
+ */
+ scale = (v2_code_table[mid].temp - v2_code_table[mid - 1].temp) /
+ (v2_code_table[mid - 1].code - v2_code_table[mid].code);
+ return v2_code_table[mid - 1].temp +
+ (v2_code_table[mid - 1].code - code) * scale;
}

/**
--
1.9.1


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