Re: [PATCH 1/2] thermal: qcom: tsens: atomic temperature read with hardware-guided retries

[Priyansh Jain <priyansh.jain@oss.qualcomm.com>]

On 05-05-2026 03:05 pm, Daniel Lezcano wrote:
> On 5/5/26 10:48, Priyansh Jain wrote:
> 
> [ ... ]
> 
>>>>>
>>>>> int prev = INTMAX;
>>>>>
>>>>> /*
>>>>>   * An explanation ...
>>>>>   */
>>>>>
>>>>> for (i = 0; i < max_retry; i++) {
>>>>>
>>>>>      int value, valid;
>>>>>
>>>>>      ret = regmap_field_read(priv->rf[field], &status);
>>>>>      if (ret)
>>>>>          return ret;
>>>>>
>>>>>      value = FIELD_GET(priv->feat->last_temp_mask, status);
>>>>>
>>>>>      valid = FIELD_GET(priv->feat->valid_bit, status)
>>>>>      if (valid)
>>>>>          return value;
>>>>>
>>>>>      if (value == prev)
>>>>>          return value;
>>>>>
>>>>>      prev = value;
>>>>> }
>>>>>
>>>>> return -EAGAIN;
>>>>>
>>>>> (Not tested)
>>>> This approach has some misalignment with the HW recommendations.
>>>> As per the HW guidelines, 3 back‑to‑back reads must be performed 
>>>> until a valid read is observed.
>>>> b or c should be returned only if none of the three reads(a,b,c) 
>>>> report the valid bit not set.
>>>
>>> Right I missed the point the HW recommendations is to read 3 times in 
>>> any case. Maybe replace if (value == prev) continue; ?
>>>
>> We need to store all three readings because, if all of them are 
>> invalid, we must compare the first, second, and third reads using the 
>> following logic:
>>
>> if a == b, return b
>> else if b == c, return c
>> else return -EAGAIN
>>
>> Given this requirement, comparing (value == prev) inside the read loop 
>> would not be correct, as it does not preserve all three samples for 
>> the final comparison.
> 
> I tried the different combinations and comparing inside the loop should 
> work. But the optimization introduces an implicit inference not helping 
> for the clarity of the code and probably prone to errors in case of 
> changes. So probably simpler to keep your approach. Please add a comment 
> above the if a == b return b else ...
> 
> Thanks

Thanks , will go ahead with my approach and will add a comment before 
comparison code .

Thanks,
Priyansh

> 
>    -- Daniel