[PATCH] thermal: generic-adc: Fix linear temperature approximation

[PATCH] thermal: generic-adc: Fix linear temperature approximation

[Paweł Jarosz]

In current version of the driver there is error in temperature
calculation.

So lets fix it using proper linear function.

Signed-off-by: Paweł Jarosz <paweljarosz3691@gmail.com>
---
 drivers/thermal/thermal-generic-adc.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/thermal/thermal-generic-adc.c b/drivers/thermal/thermal-generic-adc.c
index 73f55d6..1190aee 100644
--- a/drivers/thermal/thermal-generic-adc.c
+++ b/drivers/thermal/thermal-generic-adc.c
@@ -26,7 +26,7 @@ struct gadc_thermal_info {
 
 static int gadc_thermal_adc_to_temp(struct gadc_thermal_info *gti, int val)
 {
-	int temp, adc_hi, adc_lo;
+	int temp, adc1, adc2, temp1, temp2;
 	int i;
 
 	for (i = 0; i < gti->nlookup_table; i++) {
@@ -39,10 +39,13 @@ static int gadc_thermal_adc_to_temp(struct gadc_thermal_info *gti, int val)
 	} else if (i >= (gti->nlookup_table - 1)) {
 		temp = gti->lookup_table[2 * (gti->nlookup_table - 1)];
 	} else {
-		adc_hi = gti->lookup_table[2 * i - 1];
-		adc_lo = gti->lookup_table[2 * i + 1];
-		temp = gti->lookup_table[2 * i];
-		temp -= ((val - adc_lo) * 1000) / (adc_hi - adc_lo);
+		adc1 = gti->lookup_table[2 * i - 1];
+		adc2 = gti->lookup_table[2 * i + 1];
+
+		temp1 = gti->lookup_table[2 * i - 2];
+		temp2 = gti->lookup_table[2 * i];
+
+		temp = (val - adc1) * (temp2 - temp1) / (adc2 - adc1) + temp1;
 	}
 
 	return temp;
-- 
2.7.4

Re: [PATCH] thermal: generic-adc: Fix linear temperature approximation

[Laxman Dewangan]

On Wednesday 19 October 2016 01:01 AM, Paweł Jarosz wrote:
> In current version of the driver there is error in temperature
> calculation.
>
> So lets fix it using proper linear function.
>
> Signed-off-by: Paweł Jarosz <paweljarosz3691@gmail.com>

Per my calculation, existing and your equation is same as both are doing 
linear interpolation.

Only think I have seen is that I have used 1000 for two consecutive temp 
difference and you used (t2 - t1), so your is better in this case but 
still the equation is same.

The equation from you is

     t1 + (hi -val) * factor.

and existing one is
      t2 - (val -lo) * factor


factor is abs((t2-t1)/(hi-lo))

If my analysis is not correct then can you please provide the example 
with calculation for better understansing?


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Re: [PATCH] thermal: generic-adc: Fix linear temperature approximation

[Paweł Jarosz]

W dniu 20.10.2016 o 14:40, Laxman Dewangan pisze:
>
> On Wednesday 19 October 2016 01:01 AM, Paweł Jarosz wrote:
>> In current version of the driver there is error in temperature
>> calculation.
>>
>> So lets fix it using proper linear function.
>>
>> Signed-off-by: Paweł Jarosz <paweljarosz3691@gmail.com>
>
> Per my calculation, existing and your equation is same as both are 
> doing linear interpolation.
>
> Only think I have seen is that I have used 1000 for two consecutive 
> temp difference and you used (t2 - t1), so your is better in this case 
> but still the equation is same.
>
> The equation from you is
>
>     t1 + (hi -val) * factor.
>
> and existing one is
>      t2 - (val -lo) * factor
>
>
> factor is abs((t2-t1)/(hi-lo))
>
> If my analysis is not correct then can you please provide the example 
> with calculation for better understansing?

Hi

For example if we try to calculate temp for val = 8, i = 1 and table:

<0 9
  2 7>

	adc_hi = gti->lookup_table[2 * i - 1];
	adc_lo = gti->lookup_table[2 * i + 1];
	temp = gti->lookup_table[2 * i];
	temp -= ((val - adc_lo) * 1000) / (adc_hi - adc_lo);

Your method gives temp =  -498

Paweł

Re: [PATCH] thermal: generic-adc: Fix linear temperature approximation

[Laxman Dewangan]

On Thursday 20 October 2016 08:26 PM, Paweł Jarosz wrote:
>
>
> W dniu 20.10.2016 o 14:40, Laxman Dewangan pisze:
>>
>> On Wednesday 19 October 2016 01:01 AM, Paweł Jarosz wrote:
>>> In current version of the driver there is error in temperature
>>> calculation.
>>>
>>> So lets fix it using proper linear function.
>>>
>>> Signed-off-by: Paweł Jarosz <paweljarosz3691@gmail.com>
>>
>> Per my calculation, existing and your equation is same as both are 
>> doing linear interpolation.
>>
>> Only think I have seen is that I have used 1000 for two consecutive 
>> temp difference and you used (t2 - t1), so your is better in this 
>> case but still the equation is same.
>>
>> The equation from you is
>>
>>     t1 + (hi -val) * factor.
>>
>> and existing one is
>>      t2 - (val -lo) * factor
>>
>>
>> factor is abs((t2-t1)/(hi-lo))
>>
>> If my analysis is not correct then can you please provide the example 
>> with calculation for better understansing?
>
> Hi
>
> For example if we try to calculate temp for val = 8, i = 1 and table:
>
> <0 9
>  2 7>
>
>     adc_hi = gti->lookup_table[2 * i - 1];
>     adc_lo = gti->lookup_table[2 * i + 1];
>     temp = gti->lookup_table[2 * i];
>     temp -= ((val - adc_lo) * 1000) / (adc_hi - adc_lo);
>
> Your method gives temp =  -498
>
>


The temp should be in the milli-centigrade in the table so it should be
<0 9
   2000 7>;

and if you relplace 1000 with the t2 -t1 where

t1  = gti->lookup_table[2*i -2]
t2 = gti->lookup_table[2 *i]

then it will work perfectly.

So your change for replacing 1000 is correct as what I said but need not 
to change whole equation altogether.

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Re: [PATCH] thermal: generic-adc: Fix linear temperature approximation

[Paweł Jarosz]

W dniu 20.10.2016 o 17:49, Laxman Dewangan pisze:
>
> On Thursday 20 October 2016 08:26 PM, Paweł Jarosz wrote:
>>
>>
>> W dniu 20.10.2016 o 14:40, Laxman Dewangan pisze:
>>>
>>> On Wednesday 19 October 2016 01:01 AM, Paweł Jarosz wrote:
>>>> In current version of the driver there is error in temperature
>>>> calculation.
>>>>
>>>> So lets fix it using proper linear function.
>>>>
>>>> Signed-off-by: Paweł Jarosz <paweljarosz3691@gmail.com>
>>>
>>> Per my calculation, existing and your equation is same as both are 
>>> doing linear interpolation.
>>>
>>> Only think I have seen is that I have used 1000 for two consecutive 
>>> temp difference and you used (t2 - t1), so your is better in this 
>>> case but still the equation is same.
>>>
>>> The equation from you is
>>>
>>>     t1 + (hi -val) * factor.
>>>
>>> and existing one is
>>>      t2 - (val -lo) * factor
>>>
>>>
>>> factor is abs((t2-t1)/(hi-lo))
>>>
>>> If my analysis is not correct then can you please provide the 
>>> example with calculation for better understansing?
>>
>> Hi
>>
>> For example if we try to calculate temp for val = 8, i = 1 and table:
>>
>> <0 9
>>  2 7>
>>
>>     adc_hi = gti->lookup_table[2 * i - 1];
>>     adc_lo = gti->lookup_table[2 * i + 1];
>>     temp = gti->lookup_table[2 * i];
>>     temp -= ((val - adc_lo) * 1000) / (adc_hi - adc_lo);
>>
>> Your method gives temp =  -498
>>
>>
>
>
> The temp should be in the milli-centigrade in the table so it should be
> <0 9
>   2000 7>;
>
> and if you relplace 1000 with the t2 -t1 where
>
> t1  = gti->lookup_table[2*i -2]
> t2 = gti->lookup_table[2 *i]
>
> then it will work perfectly.
>
> So your change for replacing 1000 is correct as what I said but need 
> not to change whole equation altogether.

Sorry for that ... when i was writing this i wasn't using your equation, 
but writing from scratch.
I can send new patch with corrections or leave it as it is. Your call.


Paweł

Re: [PATCH] thermal: generic-adc: Fix linear temperature approximation

[Laxman Dewangan]

On Thursday 20 October 2016 09:44 PM, Paweł Jarosz wrote:
>
>
> W dniu 20.10.2016 o 17:49, Laxman Dewangan pisze:
>>
>> On Thursday 20 October 2016 08:26 PM, Paweł Jarosz wrote:
>>>
>>>
>>> W dniu 20.10.2016 o 14:40, Laxman Dewangan pisze:
>>>>
>>>> On Wednesday 19 October 2016 01:01 AM, Paweł Jarosz wrote:
>>>>> In current version of the driver there is error in temperature
>>>>> calculation.
>>>>>
>>>>> So lets fix it using proper linear function.
>>>>>
>>>>> Signed-off-by: Paweł Jarosz <paweljarosz3691@gmail.com>
>>>>
>>>> Per my calculation, existing and your equation is same as both are 
>>>> doing linear interpolation.
>>>>
>>>> Only think I have seen is that I have used 1000 for two consecutive 
>>>> temp difference and you used (t2 - t1), so your is better in this 
>>>> case but still the equation is same.
>>>>
>>>> The equation from you is
>>>>
>>>>     t1 + (hi -val) * factor.
>>>>
>>>> and existing one is
>>>>      t2 - (val -lo) * factor
>>>>
>>>>
>>>> factor is abs((t2-t1)/(hi-lo))
>>>>
>>>> If my analysis is not correct then can you please provide the 
>>>> example with calculation for better understansing?
>>>
>>> Hi
>>>
>>> For example if we try to calculate temp for val = 8, i = 1 and table:
>>>
>>> <0 9
>>>  2 7>
>>>
>>>     adc_hi = gti->lookup_table[2 * i - 1];
>>>     adc_lo = gti->lookup_table[2 * i + 1];
>>>     temp = gti->lookup_table[2 * i];
>>>     temp -= ((val - adc_lo) * 1000) / (adc_hi - adc_lo);
>>>
>>> Your method gives temp =  -498
>>>
>>>
>>
>>
>> The temp should be in the milli-centigrade in the table so it should be
>> <0 9
>>   2000 7>;
>>
>> and if you relplace 1000 with the t2 -t1 where
>>
>> t1  = gti->lookup_table[2*i -2]
>> t2 = gti->lookup_table[2 *i]
>>
>> then it will work perfectly.
>>
>> So your change for replacing 1000 is correct as what I said but need 
>> not to change whole equation altogether.
>
> Sorry for that ... when i was writing this i wasn't using your 
> equation, but writing from scratch.
> I can send new patch with corrections or leave it as it is. Your call.
>
>
Yes please send patch to replace the 1000 with the temp1 - temp2 as what 
you did in your original patch.
This will fix the non-sequenced (un-equally spaced) temperature table.

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Re: [PATCH] thermal: generic-adc: Fix linear temperature approximation

[Paweł Jarosz]

> Yes please send patch to replace the 1000 with the temp1 - temp2 as 
> what you did in your original patch.
> This will fix the non-sequenced (un-equally spaced) temperature table.

replacing 1000 with (temp1 - temp2) is not enough as for example for val 
= 9 and table

<7000 8
  9000 10>

	adc_hi = gti->lookup_table[2 * i - 1];
	adc_lo = gti->lookup_table[2 * i + 1];
	temp = gti->lookup_table[2 * i];
	temp -= (val - adc_lo) * (temp1 - temp2) / (adc_hi - adc_lo);


adc_hi = 8
adc_lo = 10
temp = 9000 - (9 - 10) * (7000 - 9000) / (8 - 10)
temp = 9000 - (-1) * (-2000) / (-2)
temp = 9000 - (-1000) = 10000

and for val = 9 temp should be 8000.

Re: [PATCH] thermal: generic-adc: Fix linear temperature approximation

[Laxman Dewangan]

On Thursday 20 October 2016 10:40 PM, Paweł Jarosz wrote:
>
>> Yes please send patch to replace the 1000 with the temp1 - temp2 as 
>> what you did in your original patch.
>> This will fix the non-sequenced (un-equally spaced) temperature table.
>
> replacing 1000 with (temp1 - temp2) is not enough as for example for 
> val = 9 and table
>
> <7000 8
>  9000 10>


It is Negative Coefficient Thermistor (NCT) and so adc reads are different.
Lower temp gives higher value.

So table should be

<7000 10
9000 8>;

temp1 = gti->lookup_table[2 * i];
temp2 = gti->lookup_table[2 * i - 2];

and then use in following equation.

>
>     adc_hi = gti->lookup_table[2 * i - 1];
>     adc_lo = gti->lookup_table[2 * i + 1];
>     temp = gti->lookup_table[2 * i];
>     temp -= (val - adc_lo) * (temp1 - temp2) / (adc_hi - adc_lo);
>
>

> adc_hi = 8
> adc_lo = 10
> temp = 9000 - (9 - 10) * (7000 - 9000) / (8 - 10)
> temp = 9000 - (-1) * (-2000) / (-2)
> temp = 9000 - (-1000) = 10000
>
> and for val = 9 temp should be 8000.
>
>

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Re: [PATCH] thermal: generic-adc: Fix linear temperature approximation

[Paweł Jarosz]

> It is Negative Coefficient Thermistor (NCT) and so adc reads are 
> different.
> Lower temp gives higher value.
>
> So table should be
>
> <7000 10
> 9000 8>;
>
> temp1 = gti->lookup_table[2 * i];
> temp2 = gti->lookup_table[2 * i - 2];
>
> and then use in following equation.
>
>>
>>     adc_hi = gti->lookup_table[2 * i - 1];
>>     adc_lo = gti->lookup_table[2 * i + 1];
>>     temp = gti->lookup_table[2 * i];
>>     temp -= (val - adc_lo) * (temp1 - temp2) / (adc_hi - adc_lo);

val = 9
adc_hi = 10
adc_lo = 8
temp = 9000 - (9 - 8)*(7000 - 9000)/(10 - 8)
temp = 9000 - (1)*(-2000)/(2)

temp = 9000 - (-1000) = 10000

still wrong ... temp for val = 9 should be 8000

Maybe we could leave this patch as it is?


Paweł

Re: [PATCH] thermal: generic-adc: Fix linear temperature approximation

[Laxman Dewangan]

On Thursday 20 October 2016 10:56 PM, Paweł Jarosz wrote:
>
>> It is Negative Coefficient Thermistor (NCT) and so adc reads are 
>> different.
>> Lower temp gives higher value.
>>
>> So table should be
>>
>> <7000 10
>> 9000 8>;
>>
>> temp1 = gti->lookup_table[2 * i];
>> temp2 = gti->lookup_table[2 * i - 2];
>>
>> and then use in following equation.
>>
>>>
>>>     adc_hi = gti->lookup_table[2 * i - 1];
>>>     adc_lo = gti->lookup_table[2 * i + 1];
>>>     temp = gti->lookup_table[2 * i];
>>>     temp -= (val - adc_lo) * (temp1 - temp2) / (adc_hi - adc_lo);
>
> val = 9
> adc_hi = 10
> adc_lo = 8
> temp = 9000 - (9 - 8)*(7000 - 9000)/(10 - 8)
> temp = 9000 - (1)*(-2000)/(2)
>
> temp = 9000 - (-1000) = 10000
>
> still wrong ... temp for val = 9 should be 8000


Your temp1 and temp2 calculation is something wrong.

temp1 = gti->lookup_table[2 * i];
temp2 = gti->lookup_table[2 * i - 2];
so temp1 = 9000, temp2 = 7000

temp -= (val - adc_lo) * (temp1 - temp2) / (adc_hi - adc_lo);

temp = 9000 - (9 - 8)*(9000 - 7000)/(10 - 8)
temp = 9000 - (1)*(2000)/(2) = 8000 which is expected.



>
> Maybe we could leave this patch as it is?
>


temp = gti->lookup_table[2 * i];
+ tlow = gti->lookup_table[2 * i - 2];
(modify) temp -= (val - adc_lo) * (temp - tlow) / (adc_hi - adc_lo);

This will gives you correct result.

Let me know if you can send the updated patch. Else I will send.

Thanks,
Laxman
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Re: [PATCH] thermal: generic-adc: Fix linear temperature approximation

[Paweł Jarosz]

W dniu 21.10.2016 o 08:18, Laxman Dewangan pisze:
>
> On Thursday 20 October 2016 10:56 PM, Paweł Jarosz wrote:
>>
>>> It is Negative Coefficient Thermistor (NCT) and so adc reads are 
>>> different.
>>> Lower temp gives higher value.
>>>
>>> So table should be
>>>
>>> <7000 10
>>> 9000 8>;
>>>
>>> temp1 = gti->lookup_table[2 * i];
>>> temp2 = gti->lookup_table[2 * i - 2];
>>>
>>> and then use in following equation.
>>>
>>>>
>>>>     adc_hi = gti->lookup_table[2 * i - 1];
>>>>     adc_lo = gti->lookup_table[2 * i + 1];
>>>>     temp = gti->lookup_table[2 * i];
>>>>     temp -= (val - adc_lo) * (temp1 - temp2) / (adc_hi - adc_lo);
>>
>> val = 9
>> adc_hi = 10
>> adc_lo = 8
>> temp = 9000 - (9 - 8)*(7000 - 9000)/(10 - 8)
>> temp = 9000 - (1)*(-2000)/(2)
>>
>> temp = 9000 - (-1000) = 10000
>>
>> still wrong ... temp for val = 9 should be 8000
>
>
> Your temp1 and temp2 calculation is something wrong.
>
> temp1 = gti->lookup_table[2 * i];
> temp2 = gti->lookup_table[2 * i - 2];
> so temp1 = 9000, temp2 = 7000
>
There was nothing wrong with my calculation but you changed the order to 
fix your equation.

You can send the patch.


Paweł