Re: [PATCH] TSL2550 driver bugfix

[Jonathan Cameron <jic23-KWPb1pKIrIJaa/9Udqfwiw@public.gmane.org>]

> What do you think about 'Bugfix for missing Lux returning in dark
> environment' ?
That covers the key point, so fine.
 
> Jonathan Cameron wrote:
>> Looks good to me. (perhaps a bit more detail in the commit
>> message of the patch?)
>>
>> Acked-by: Jonathan Cameron <jic23-KWPb1pKIrIJaa/9Udqfwiw@public.gmane.org>
>>  
>>> Jonathan Cameron wrote:
>>>    
>>>> Michele De Candia (VT) wrote:
>>>>  
>>>>      
>>>>> Hi all,
>>>>>
>>>>> I've tested TSL2550 driver and I've found a bug: when light is off,
>>>>> returned value from tsl2550_calculate_lux function is -1 when it
>>>>> should
>>>>> be 0 (sensor correctly read that light was off).
>>>>>
>>>>> I think the bug is that a zero c0 value (approximated value of ch0) is
>>>>> misinterpreted as an error.
>>>>> I'm attaching you a patch that fixes the bug.
>>>>>
>>>>> Regards,
>>>>> Michele Jr De Candia
>>>>>             
>>>> Sounds reasonable, but I think a stray line got away in your patch
>>>> (see below)
>>>> Not to mention, if the c1 <= c0 check is still valid, should you not
>>>> also
>>>> confirm that c1 == 0 as well? Perhaps reverse the ordering?
>>>>         
>>> That's right. A new patch can be found in attachment.
>>>    
>>>> if (c1 <= c0)
>>>>     if(c0) {
>>>>         r = c1* 128 / c0;
>>>>         lux = ((c0 - c1) * ratio_lut[r]) / 256;
>>>>     } else
>>>>         lux = 0;
>>>> else
>>>>     return -1;
>>>>    
>>>> Signed-off-by: Michele Jr De Candia <michele.decandia-EZxuzQJkuwwybS5Ee8rs3A@public.gmane.org>
>>>>
>>>> diff --git a/drivers/i2c/chips/tsl2550.c b/drivers/i2c/chips/tsl2550.c
>>>> index 1a9cc13..6bad072 100644
>>>> --- a/drivers/i2c/chips/tsl2550.c
>>>> +++ b/drivers/i2c/chips/tsl2550.c
>>>> @@ -189,10 +189,16 @@ static int tsl2550_calculate_lux(u8 ch0, u8 ch1)
>>>>      u8 r = 128;
>>>>  
>>>>      /* Avoid division by 0 and count 1 cannot be greater than count
>>>> 0 */
>>>> -    if (c0 && (c1 <= c0))
>>>> -        r = c1 * 128 / c0;
>>>> -    else
>>>> -        return -1;
>>>> +    if (c0)    {
>>>> +        if (c1 <= c0)
>>>> +            r = c1 * 128 / c0;
>>>> +        else
>>>> +            return -1;
>>>> +           +        /* Calculate LUX */
>>>> +        lux = ((c0 - c1) * ratio_lut[r]) / 256;
>>>> +    }
>>>> +    else lux = 0;
>>>>  
>>>>
>>>> This last line should have been removed I think?
>>>>      /* Calculate LUX */
>>>>     lux = ((c0 - c1) * ratio_lut[r]) / 256;
>>>>
>>>> ---
>>>> Jonathan Cameron
>>>>
>>>>         
>>> Than
>>>     
>>
>>   
> 
>