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

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

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

Konrad