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SAI Switch Temperature Attributes for Sub-degree Precision #2306

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SAI Switch Temperature Attributes for Sub-degree Precision #2306

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26 changes: 26 additions & 0 deletions inc/saiswitch.h
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Expand Up @@ -3616,6 +3616,32 @@ typedef enum _sai_switch_attr_t
*/
SAI_SWITCH_ATTR_PERFMON_LIST,

/**
* @brief List of raw (non-rounded) temperature readings from all sensors.
*
* Values should be interpreted along with SAI_SWITCH_ATTR_TEMP_BASE_TEN_PRECISION.
* Companion to SAI_SWITCH_ATTR_TEMP_LIST (which returns rounded Celsius).
*
* @type sai_s32_list_t
* @flags READ_ONLY
*/

@jjin62 jjin62 Jun 30, 2026

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The commit added a new tag @precision. You can define the precision in SAI_SWITCH_ATTR_TEMP_LIST_RAW and no need SAI_SWITCH_ATTR_TEMP_BASE_TEN_PRECISION. You can get the precision from the meta data attr->valuePrecision.
See the examples in https://github.com/opencomputeproject/SAI/blob/master/experimental/saiexperimentalotnoa.h

@bp899348 bp899348 Jun 30, 2026

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Thank you for the suggestion. The @precision tag is a compile-time constant in the metadata — it is hardcoded at attribute definition time and cannot change at runtime.

In our case, the temperature resolution is hardware and platform dependent and must be queried at runtime. SAI_SWITCH_ATTR_TEMP_BASE_TEN_PRECISION is a READ_ONLY attribute that the driver reports dynamically, allowing consumers to adapt without any code or metadata change as platforms evolve.

So yes, @precision would still be hardcoded — just in a different place.

@jjin62 jjin62 Jun 30, 2026 •
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I see. But we can always put a conservative @precision, like 6 to cover all the vendors. Two attributes for one value implies much semantics and is error prone. Just my 2 cents.

@bp899348 bp899348 Jul 8, 2026

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I understand the point, but a conservative fixed @precision like 6 means every consumer always multiplies by 10^-6 - even when the hardware only reports tenths of a degree. This would silently produce incorrect values on platforms that don't match that precision, with no way to detect the mismatch at runtime.
With SAI_SWITCH_ATTR_TEMP_BASE_TEN_PRECISION, the driver reports exactly what the hardware delivers — no guessing, no silent error. The cost is one extra attribute query; the benefit is guaranteed correctness across all platforms without any consumer-side assumptions.

SAI_SWITCH_ATTR_TEMP_LIST_RAW,

/**
* @brief Power-of-10 exponent for raw temperature precision.
*
* Defines the scale of values in SAI_SWITCH_ATTR_TEMP_LIST_RAW.
* Formula: actual_celsius = raw_value * (10 ^ precision)
* Examples:
* precision = 0 => values already in whole Celsius (same as TEMP_LIST)
* precision = -1 => values in 0.1 degrees C steps (445 = 44.5 degrees C)
* precision = -2 => values in 0.01 degrees C steps
*
* @type sai_int8_t
* @flags READ_ONLY
*/
SAI_SWITCH_ATTR_TEMP_BASE_TEN_PRECISION,

/**
* @brief End of attributes
*/
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