dpll: add phase-offset-avg-factor device attribute to netlink spec

Add dpll device level attribute DPLL_A_PHASE_OFFSET_AVG_FACTOR to allow
control over a calculation of reported phase offset value. Attribute is
present, if the driver provides such capability, otherwise attribute
shall not be present.

Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Link: https://patch.msgid.link/20250927084912.2343597-2-ivecera@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/driver-api/dpll.rst

@@ -179,7 +179,23 @@ Phase offset measurement and adjustment
 Device may provide ability to measure a phase difference between signals
 on a pin and its parent dpll device. If pin-dpll phase offset measurement
 is supported, it shall be provided with ``DPLL_A_PIN_PHASE_OFFSET``
-attribute for each parent dpll device.
+attribute for each parent dpll device. The reported phase offset may be
+computed as the average of prior values and the current measurement, using
+the following formula:
+
+.. math::
+   curr\_avg = prev\_avg * \frac{2^N-1}{2^N} + new\_val * \frac{1}{2^N}
+
+where `curr_avg` is the current reported phase offset, `prev_avg` is the
+previously reported value, `new_val` is the current measurement, and `N` is
+the averaging factor. Configured averaging factor value is provided with
+``DPLL_A_PHASE_OFFSET_AVG_FACTOR`` attribute of a device and value change can
+be requested with the same attribute with ``DPLL_CMD_DEVICE_SET`` command.
+
+  ================================== ======================================
+  ``DPLL_A_PHASE_OFFSET_AVG_FACTOR`` attr configured value of phase offset
+                                     averaging factor
+  ================================== ======================================
 
 Device may also provide ability to adjust a signal phase on a pin.
 If pin phase adjustment is supported, minimal and maximal values that pin

Documentation/netlink/specs/dpll.yaml

@@ -315,6 +315,10 @@ attribute-sets:
           If enabled, dpll device shall monitor and notify all currently
           available inputs for changes of their phase offset against the
           dpll device.
+      -
+        name: phase-offset-avg-factor
+        type: u32
+        doc: Averaging factor applied to calculation of reported phase offset.
   -
     name: pin
     enum-name: dpll_a_pin
@@ -523,6 +527,7 @@ operations:
             - clock-id
             - type
             - phase-offset-monitor
+            - phase-offset-avg-factor
 
       dump:
         reply: *dev-attrs
@@ -540,6 +545,7 @@ operations:
           attributes:
             - id
             - phase-offset-monitor
+            - phase-offset-avg-factor
     -
       name: device-create-ntf
       doc: Notification about device appearing

drivers/dpll/dpll_nl.c

@@ -42,9 +42,10 @@ static const struct nla_policy dpll_device_get_nl_policy[DPLL_A_ID + 1] = {
 };
 
 /* DPLL_CMD_DEVICE_SET - do */
-static const struct nla_policy dpll_device_set_nl_policy[DPLL_A_PHASE_OFFSET_MONITOR + 1] = {
+static const struct nla_policy dpll_device_set_nl_policy[DPLL_A_PHASE_OFFSET_AVG_FACTOR + 1] = {
 	[DPLL_A_ID] = { .type = NLA_U32, },
 	[DPLL_A_PHASE_OFFSET_MONITOR] = NLA_POLICY_MAX(NLA_U32, 1),
+	[DPLL_A_PHASE_OFFSET_AVG_FACTOR] = { .type = NLA_U32, },
 };
 
 /* DPLL_CMD_PIN_ID_GET - do */
@@ -112,7 +113,7 @@ static const struct genl_split_ops dpll_nl_ops[] = {
 		.doit		= dpll_nl_device_set_doit,
 		.post_doit	= dpll_post_doit,
 		.policy		= dpll_device_set_nl_policy,
-		.maxattr	= DPLL_A_PHASE_OFFSET_MONITOR,
+		.maxattr	= DPLL_A_PHASE_OFFSET_AVG_FACTOR,
 		.flags		= GENL_ADMIN_PERM | GENL_CMD_CAP_DO,
 	},
 	{

include/uapi/linux/dpll.h

@@ -216,6 +216,7 @@ enum dpll_a {
 	DPLL_A_LOCK_STATUS_ERROR,
 	DPLL_A_CLOCK_QUALITY_LEVEL,
 	DPLL_A_PHASE_OFFSET_MONITOR,
+	DPLL_A_PHASE_OFFSET_AVG_FACTOR,
 
 	__DPLL_A_MAX,
 	DPLL_A_MAX = (__DPLL_A_MAX - 1)