Re: [PATCH v2 1/2] thermal: qcom: tsens: atomic temperature read with hardware-guided retries

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

On 08-05-2026 05:39 pm, Konrad Dybcio wrote:
> On 5/8/26 12:06 PM, Priyansh Jain wrote:
>> The existing TSENS temperature read logic polls the valid bit and then
>> reads the temperature register. When temperature reads are triggered
>> at very short intervals, this can race with hardware updates and allow
>> the temperature field to be read while it is still being updated.
>>
>> In this case, the valid bit may already be asserted even though the
>> temperature value is transitioning, resulting in an incorrect reading.
>>
>> Hardware programming guidelines require the temperature value and the
>> valid bit to be sampled atomically in the same read transaction. A
>> reading is considered valid only if the valid bit is observed set in
>> that same sample.
>>
>> The guidelines further specify that software should attempt the
>> temperature read up to three times to account for transient update
>> windows. If none of the attempts observe a valid sample, a stable
>> fallback value must be returned: if the first and second samples match,
>> the second value is returned; otherwise, if the second and third
>> samples match, the third value is returned.
>>
>> Update the TSENS sensor read logic to implement atomic sampling along
>> with the recommended retry-and-compare fallback behavior. This removes
>> the race window and ensures deterministic temperature values in
>> accordance with hardware requirements.
>>
>> Signed-off-by: Priyansh Jain <priyansh.jain@oss.qualcomm.com>
>> ---
> 
> [...]
> 
>>   struct tsens_features {
>>   	unsigned int ver_major;
>> @@ -522,6 +526,9 @@ struct tsens_features {
>>   	unsigned int max_sensors;
>>   	int trip_min_temp;
>>   	int trip_max_temp;
>> +	int valid_bit;
>> +	int last_temp_mask;
>> +	u32 last_temp_resolution;
> 
> You don't need this now that you aren't altering the regfield
> definitions
> 
Yes, that's correct. Thanks for pointing this out — I will update the 
code accordingly in the next patch version.

Thanks,
Priyansh

> Konrad