[PATCH net-next] dpll: expose fractional frequency offset in ppt

[Ivan Vecera <ivecera@redhat.com>]

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 <ivecera@redhat.com>
---
 Documentation/netlink/specs/dpll.yaml          | 11 +++++++++++
 drivers/dpll/dpll_netlink.c                    | 10 +++++++++-
 drivers/dpll/zl3073x/core.c                    |  7 +++++--
 drivers/net/ethernet/mellanox/mlx5/core/dpll.c |  2 +-
 include/uapi/linux/dpll.h                      |  1 +
 5 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/Documentation/netlink/specs/dpll.yaml b/Documentation/netlink/specs/dpll.yaml
index b55afa77eac4b..3dd48a32f7837 100644
--- a/Documentation/netlink/specs/dpll.yaml
+++ b/Documentation/netlink/specs/dpll.yaml
@@ -446,6 +446,16 @@ attribute-sets:
         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
@@ -628,6 +638,7 @@ operations:
             - phase-adjust-max
             - phase-adjust
             - fractional-frequency-offset
+            - fractional-frequency-offset-ppt
             - esync-frequency
             - esync-frequency-supported
             - esync-pulse
diff --git a/drivers/dpll/dpll_netlink.c b/drivers/dpll/dpll_netlink.c
index 499bca460b1e1..904199ddd1781 100644
--- a/drivers/dpll/dpll_netlink.c
+++ b/drivers/dpll/dpll_netlink.c
@@ -389,7 +389,15 @@ static int dpll_msg_add_ffo(struct sk_buff *msg, struct dpll_pin *pin,
 			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
diff --git a/drivers/dpll/zl3073x/core.c b/drivers/dpll/zl3073x/core.c
index 383e2397dd033..63bd97181b9ee 100644
--- a/drivers/dpll/zl3073x/core.c
+++ b/drivers/dpll/zl3073x/core.c
@@ -710,8 +710,11 @@ zl3073x_ref_ffo_update(struct zl3073x_dev *zldev)
 		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;
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/dpll.c b/drivers/net/ethernet/mellanox/mlx5/core/dpll.c
index 1e5522a194839..3ea8a1766ae28 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/dpll.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/dpll.c
@@ -136,7 +136,7 @@ mlx5_dpll_pin_ffo_get(struct mlx5_dpll_synce_status *synce_status,
 {
 	if (!synce_status->oper_freq_measure)
 		return -ENODATA;
-	*ffo = synce_status->frequency_diff;
+	*ffo = 1000000LL * synce_status->frequency_diff;
 	return 0;
 }
 
diff --git a/include/uapi/linux/dpll.h b/include/uapi/linux/dpll.h
index b7ff9c44f9aa0..de0005f28e5c5 100644
--- a/include/uapi/linux/dpll.h
+++ b/include/uapi/linux/dpll.h
@@ -253,6 +253,7 @@ enum dpll_a_pin {
 	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)
-- 
2.52.0