Re: [PATCH v2] drm/xe/hwmon: handle CRI+ power interval encoding

On 03-07-2026 21:03, Karthik Poosa wrote:
> On CRI and newer platforms, the power-limit interval encoding is changed
> from the legacy 1.x * 2^y format to a U5.2 value in milliseconds.
> Update the interval calculation accordingly for CRI and future platforms.
>
> v2: Round the fractional bit to 1 for values greater than 0.5 ms in the
>      show path, as the minimum supported time is 1 ms.
>      No special handling is needed in the store path since sysfs inputs are
>      only in milliseconds. (Badal)
>
> Signed-off-by: Karthik Poosa <[email protected]>
Reviewed-by: Badal Nilawar <[email protected]>
> ---
>   drivers/gpu/drm/xe/xe_hwmon.c | 86 ++++++++++++++++++++++-------------
>   1 file changed, 55 insertions(+), 31 deletions(-)
>
> diff --git a/drivers/gpu/drm/xe/xe_hwmon.c b/drivers/gpu/drm/xe/xe_hwmon.c
> index de3f2aeffc3f..49f7e0edcc4b 100644
> --- a/drivers/gpu/drm/xe/xe_hwmon.c
> +++ b/drivers/gpu/drm/xe/xe_hwmon.c
> @@ -575,23 +575,36 @@ xe_hwmon_power_max_interval_show(struct device *dev, struct device_attribute *at
>   
>   	mutex_unlock(&hwmon->hwmon_lock);
>   
> -	x = REG_FIELD_GET(PWR_LIM_TIME_X, reg_val);
> -	y = REG_FIELD_GET(PWR_LIM_TIME_Y, reg_val);
> +	if (hwmon->xe->info.platform >= XE_CRESCENTISLAND) {
> +		/**
> +		 * On CRI and newer platforms, the interval encoding changed.
> +		 * The value is now stored directly in milliseconds as U5.2,
> +		 * replacing the older 1.x * 2^y representation.
> +		 * Bits [6:2] hold the integer part and bits [1:0] the fraction,
> +		 * so convert to milliseconds by extracting integer/fractional parts.
> +		 * Round fraction value to 1 when it is >= 0.5.
> +		 */
> +		reg_val = REG_FIELD_GET(PWR_LIM_TIME, reg_val);
> +		out = (u64)((reg_val >> 2) + ((reg_val & 0x3) >= 2));
> +	} else {
> +		x = REG_FIELD_GET(PWR_LIM_TIME_X, reg_val);
> +		y = REG_FIELD_GET(PWR_LIM_TIME_Y, reg_val);
>   
> -	/*
> -	 * tau = (1 + (x / 4)) * power(2,y), x = bits(23:22), y = bits(21:17)
> -	 *     = (4 | x) << (y - 2)
> -	 *
> -	 * Here (y - 2) ensures a 1.x fixed point representation of 1.x
> -	 * As x is 2 bits so 1.x can be 1.0, 1.25, 1.50, 1.75
> -	 *
> -	 * As y can be < 2, we compute tau4 = (4 | x) << y
> -	 * and then add 2 when doing the final right shift to account for units
> -	 */
> -	tau4 = (u64)((1 << x_w) | x) << y;
> +		/*
> +		 * tau = (1 + (x / 4)) * power(2,y), x = bits(23:22), y = bits(21:17)
> +		 *     = (4 | x) << (y - 2)
> +		 *
> +		 * Here (y - 2) ensures a 1.x fixed point representation of 1.x
> +		 * As x is 2 bits so 1.x can be 1.0, 1.25, 1.50, 1.75
> +		 *
> +		 * As y can be < 2, we compute tau4 = (4 | x) << y
> +		 * and then add 2 when doing the final right shift to account for units
> +		 */
> +		tau4 = (u64)((1 << x_w) | x) << y;
>   
> -	/* val in hwmon interface units (millisec) */
> -	out = mul_u64_u32_shr(tau4, SF_TIME, hwmon->scl_shift_time + x_w);
> +		/* val in hwmon interface units (millisec) */
> +		out = mul_u64_u32_shr(tau4, SF_TIME, hwmon->scl_shift_time + x_w);
> +	}
>   
>   	return sysfs_emit(buf, "%llu\n", out);
>   }
> @@ -637,24 +650,35 @@ xe_hwmon_power_max_interval_store(struct device *dev, struct device_attribute *a
>   	if (val > max_win)
>   		return -EINVAL;
>   
> -	/* val in hw units */
> -	val = DIV_ROUND_CLOSEST_ULL((u64)val << hwmon->scl_shift_time, SF_TIME) + 1;
> -
> -	/*
> -	 * Convert val to 1.x * power(2,y)
> -	 * y = ilog2(val)
> -	 * x = (val - (1 << y)) >> (y - 2)
> -	 */
> -	if (!val) {
> -		y = 0;
> -		x = 0;
> +	if (hwmon->xe->info.platform >= XE_CRESCENTISLAND) {
> +		/**
> +		 * On CRI and newer platforms, the interval encoding changed.
> +		 * The value is now stored directly in milliseconds as U5.2,
> +		 * replacing the older 1.x * 2^y representation.
> +		 * Bits [6:2] hold the integer part and bits [1:0] the fraction,so
> +		 * convert from milliseconds by shifting the value left by 2 to fit into the field.
> +		 */
> +		rxy = REG_FIELD_PREP(PWR_LIM_TIME, (val << 2));
>   	} else {
> -		y = ilog2(val);
> -		x = (val - (1ul << y)) << x_w >> y;
> -	}
> +		/* val in hw units */
> +		val = DIV_ROUND_CLOSEST_ULL((u64)val << hwmon->scl_shift_time, SF_TIME) + 1;
> +
> +		/*
> +		 * Convert val to 1.x * power(2,y)
> +		 * y = ilog2(val)
> +		 * x = (val - (1 << y)) >> (y - 2)
> +		 */
> +		if (!val) {
> +			y = 0;
> +			x = 0;
> +		} else {
> +			y = ilog2(val);
> +			x = (val - (1ul << y)) << x_w >> y;
> +		}
>   
> -	rxy = REG_FIELD_PREP(PWR_LIM_TIME_X, x) |
> -			       REG_FIELD_PREP(PWR_LIM_TIME_Y, y);
> +		rxy = REG_FIELD_PREP(PWR_LIM_TIME_X, x) |
> +				       REG_FIELD_PREP(PWR_LIM_TIME_Y, y);
> +	}
>   
>   	guard(xe_pm_runtime)(hwmon->xe);
>