dpll: expose fractional frequency offset in ppt

Currently, the dpll subsystem exports the fractional frequency offset
(FFO) in parts per million (ppm). This granularity is insufficient for
high-precision synchronization scenarios which often require parts per
trillion (ppt) resolution.

Add a new netlink attribute DPLL_A_PIN_FRACTIONAL_FREQUENCY_OFFSET_PPT
to expose the FFO in ppt.

Update the dpll netlink core to expect the driver-provided FFO value
to be in ppt. To maintain backward compatibility with existing userspace
tools, populate the legacy DPLL_A_PIN_FRACTIONAL_FREQUENCY_OFFSET
attribute by dividing the new ppt value by 1,000,000.

Update the zl3073x and mlx5 drivers to provide the FFO value in ppt:
- zl3073x: adjust the fixed-point calculation to produce ppt (10^12)
instead of ppm (10^6).
- mlx5: scale the existing ppm value by 1,000,000.

Signed-off-by: Ivan Vecera <[e-mail]>
Reviewed-by: Arkadiusz Kubalewski <[e-mail]>
Reviewed-by: Jiri Pirko <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

Documentation/netlink/specs/dpll.yaml

···
         doc: |
           Granularity of phase adjustment, in picoseconds. The value of
           phase adjustment must be a multiple of this granularity.
+      -
+        name: fractional-frequency-offset-ppt
+        type: sint
+        doc: |
+          The FFO (Fractional Frequency Offset) of the pin with respect to
+          the nominal frequency.
+          Value = (frequency_measured - frequency_nominal) / frequency_nominal
+          Value is in PPT (parts per trillion, 10^-12).
+          Note: This attribute provides higher resolution than the standard
+          fractional-frequency-offset (which is in PPM).
 
   -
     name: pin-parent-device
···
             - phase-adjust-max
             - phase-adjust
             - fractional-frequency-offset
+            - fractional-frequency-offset-ppt
             - esync-frequency
             - esync-frequency-supported
             - esync-pulse

drivers/dpll/dpll_netlink.c

···
 			return 0;
 		return ret;
 	}
-	return nla_put_sint(msg, DPLL_A_PIN_FRACTIONAL_FREQUENCY_OFFSET, ffo);
+	/* Put the FFO value in PPM to preserve compatibility with older
+	 * programs.
+	 */
+	ret = nla_put_sint(msg, DPLL_A_PIN_FRACTIONAL_FREQUENCY_OFFSET,
+			   div_s64(ffo, 1000000));
+	if (ret)
+		return -EMSGSIZE;
+	return nla_put_sint(msg, DPLL_A_PIN_FRACTIONAL_FREQUENCY_OFFSET_PPT,
+			    ffo);
 }
 
 static int

drivers/dpll/zl3073x/core.c

···
 		if (rc)
 			return rc;
 
-		/* Convert to ppm -> ffo = (10^6 * value) / 2^32 */
-		zldev->ref[i].ffo = mul_s64_u64_shr(value, 1000000, 32);
+		/* Convert to ppt
+		 * ffo = (10^12 * value) / 2^32
+		 * ffo = ( 5^12 * value) / 2^20
+		 */
+		zldev->ref[i].ffo = mul_s64_u64_shr(value, 244140625, 20);
 	}
 
 	return 0;

drivers/net/ethernet/mellanox/mlx5/core/dpll.c

···
 {
 	if (!synce_status->oper_freq_measure)
 		return -ENODATA;
-	*ffo = synce_status->frequency_diff;
+	*ffo = 1000000LL * synce_status->frequency_diff;
 	return 0;
 }
 

include/uapi/linux/dpll.h

···
 	DPLL_A_PIN_ESYNC_PULSE,
 	DPLL_A_PIN_REFERENCE_SYNC,
 	DPLL_A_PIN_PHASE_ADJUST_GRAN,
+	DPLL_A_PIN_FRACTIONAL_FREQUENCY_OFFSET_PPT,
 
 	__DPLL_A_PIN_MAX,
 	DPLL_A_PIN_MAX = (__DPLL_A_PIN_MAX - 1)