thermal: rockchip: optimize the conversion table

In order to support the valid temperature can conver to analog value.
The rockchip thermal driver has not supported the all valid temperature
to convert the analog value. (e.g.: 61C, 62C, 63C....)

For example:
In some cases, we need adjust the trip point.
$cd /sys/class/thermal/thermal_zone*
$echo 68000 > trip_point_0_temp
That will return the max analogic value indicates the invalid before
posting this patch.

So, this patch will optimize the conversion table to support the other
cases.
Signed-off-by: Caesar Wang <wxt@rock-chips.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>

drivers/thermal/rockchip_thermal.c

@@ -317,6 +317,7 @@ static const struct tsadc_table rk3288_code_table[] = {
 	{3452, 115000},
 	{3437, 120000},
 	{3421, 125000},
+	{0, 125000},
 };
 
 static const struct tsadc_table rk3368_code_table[] = {
@@ -401,10 +402,12 @@ static u32 rk_tsadcv2_temp_to_code(const struct chip_tsadc_table *table,
 				   int temp)
 {
 	int high, low, mid;
+	unsigned long num;
+	unsigned int denom;
 	u32 error = table->data_mask;
 
 	low = 0;
-	high = table->length - 1;
+	high = (table->length - 1) - 1; /* ignore the last check for table */
 	mid = (high + low) / 2;
 
 	/* Return mask code data when the temp is over table range */
@@ -421,6 +424,26 @@ static u32 rk_tsadcv2_temp_to_code(const struct chip_tsadc_table *table,
 		mid = (low + high) / 2;
 	}
 
+	/*
+	 * The conversion code granularity provided by the table. Let's
+	 * assume that the relationship between temperature and
+	 * analog value between 2 table entries is linear and interpolate
+	 * to produce less granular result.
+	 */
+	num = abs(table->id[mid + 1].code - table->id[mid].code);
+	num *= temp - table->id[mid].temp;
+	denom = table->id[mid + 1].temp - table->id[mid].temp;
+
+	switch (table->mode) {
+	case ADC_DECREMENT:
+		return table->id[mid].code - (num / denom);
+	case ADC_INCREMENT:
+		return table->id[mid].code + (num / denom);
+	default:
+		pr_err("%s: unknown table mode: %d\n", __func__, table->mode);
+		return error;
+	}
+
 exit:
 	pr_err("%s: invalid temperature, temp=%d error=%d\n",
 	       __func__, temp, error);