Add new callback operations for a dpll device:
- phase_offset_avg_factor_get(...) - to obtain current phase offset
   averaging factor from dpll device,
- phase_offset_avg_factor_set(...) - to set phase offset averaging factor

Obtain the factor value using the get callback and provide it to the user
if the device driver implements callbacks. Execute the set callback upon
user requests.

Signed-off-by: Ivan Vecera <ivecera@redhat.com>
---
  drivers/dpll/dpll_netlink.c | 76 +++++++++++++++++++++++++++++++++----
  include/linux/dpll.h        |  6 +++
  2 files changed, 75 insertions(+), 7 deletions(-)

diff --git a/drivers/dpll/dpll_netlink.c b/drivers/dpll/dpll_netlink.c
index 0a852011653c4..55b3ffe08024b 100644
--- a/drivers/dpll/dpll_netlink.c
+++ b/drivers/dpll/dpll_netlink.c

@@ -164,6 +164,28 @@ dpll_msg_add_phase_offset_monitor(struct sk_buff *msg, struct dpll_device *dpll,
  	return 0;
  }
  
+static int
+dpll_msg_add_phase_offset_avg_factor(struct sk_buff *msg,
+				     struct dpll_device *dpll,
+				     struct netlink_ext_ack *extack)
+{
+	const struct dpll_device_ops *ops = dpll_device_ops(dpll);
+	u32 factor;
+	int ret;
+
+	if (ops->phase_offset_avg_factor_set &&
+	    ops->phase_offset_avg_factor_get) {
+		ret = ops->phase_offset_avg_factor_get(dpll, dpll_priv(dpll),
+						       &factor, extack);

+		if (ret)
+			return ret;
+		if (nla_put_u32(msg, DPLL_A_PHASE_OFFSET_AVG_FACTOR, factor))
+			return -EMSGSIZE;
+	}
+
+	return 0;
+}
+
  static int
  dpll_msg_add_lock_status(struct sk_buff *msg, struct dpll_device *dpll,
  			 struct netlink_ext_ack *extack)

@@ -675,6 +697,9 @@ dpll_device_get_one(struct dpll_device *dpll, struct sk_buff *msg,
  	if (nla_put_u32(msg, DPLL_A_TYPE, dpll->type))
  		return -EMSGSIZE;
  	ret = dpll_msg_add_phase_offset_monitor(msg, dpll, extack);
+	if (ret)
+		return ret;
+	ret = dpll_msg_add_phase_offset_avg_factor(msg, dpll, extack);
  	if (ret)
  		return ret;
  

@@ -839,6 +864,32 @@ dpll_phase_offset_monitor_set(struct dpll_device *dpll, struct nlattr *a,
  					     extack);
  }
  
+static int
+dpll_phase_offset_avg_factor_set(struct dpll_device *dpll, struct nlattr *a,
+				 struct netlink_ext_ack *extack)
+{
+	const struct dpll_device_ops *ops = dpll_device_ops(dpll);
+	u32 factor = nla_get_u32(a), old_factor;
+	int ret;
+
+	if (!(ops->phase_offset_avg_factor_set &&
+	      ops->phase_offset_avg_factor_get)) {
+		NL_SET_ERR_MSG_ATTR(extack, a, "dpll device not capable of phase offset averaging");
+		return -EOPNOTSUPP;
+	}
+	ret = ops->phase_offset_avg_factor_get(dpll, dpll_priv(dpll),
+					       &old_factor, extack);
+	if (ret) {
+		NL_SET_ERR_MSG(extack, "unable to get current phase offset averaging factor");
+		return ret;
+	}
+	if (factor == old_factor)
+		return 0;