[PATCH v4 6/7] can: netlink: add can_priv::do_get_auto_tdcv() to retrieve tdcv from device

[Vincent Mailhol <mailhol.vincent@wanadoo.fr>]

Some CAN device can measure the TDCV (Transmission Delay Compensation
Value) automatically for each transmitted CAN frames.

A callback function do_get_auto_tdcv() is added to retrieve that
value. This function is used only if CAN_CTRLMODE_TDC_AUTO is enabled
(if CAN_CTRLMODE_TDC_MANUAL is selected, the TDCV value is provided by
the user).

If the device does not support reporting of TDCV, do_get_auto_tdcv()
should be set to NULL and TDCV will not be reported by the netlink
interface.

On success, do_get_auto_tdcv() shall return 0. If the value can not be
measured by the device, for example because network is down or because
no frames were transmitted yet, can_priv::do_get_auto_tdcv() shall
return a negative error code (e.g. -EINVAL) to signify that the value
is not yet available. In such cases, TDCV is not reported by the
netlink interface.

CC: Stefan Mätje <stefan.maetje@esd.eu>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
---
 drivers/net/can/dev/netlink.c | 13 +++++++++++--
 include/linux/can/dev.h       |  1 +
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/net/can/dev/netlink.c b/drivers/net/can/dev/netlink.c
index 735b9e36202e..9164decf2ddb 100644
--- a/drivers/net/can/dev/netlink.c
+++ b/drivers/net/can/dev/netlink.c
@@ -414,8 +414,17 @@ static int can_tdc_fill_info(struct sk_buff *skb, const struct net_device *dev)
 		goto err_cancel;
 
 	if (can_tdc_is_enabled(priv)) {
-		if (priv->ctrlmode & CAN_CTRLMODE_TDC_MANUAL &&
-		    nla_put_u32(skb, IFLA_CAN_TDC_TDCV, tdc->tdcv))
+		u32 tdcv;
+		int err = -EINVAL;
+
+		if (priv->ctrlmode & CAN_CTRLMODE_TDC_MANUAL) {
+			tdcv = tdc->tdcv;
+			err = 0;
+		} else if (priv->ctrlmode & CAN_CTRLMODE_TDC_AUTO &&
+			   priv->do_get_auto_tdcv) {
+			err = priv->do_get_auto_tdcv(dev, &tdcv);
+		}
+		if (!err && nla_put_u32(skb, IFLA_CAN_TDC_TDCV, tdcv))
 			goto err_cancel;
 		if (nla_put_u32(skb, IFLA_CAN_TDC_TDCO, tdc->tdco))
 			goto err_cancel;
diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h
index fa75e29182a3..266d0fe9de9d 100644
--- a/include/linux/can/dev.h
+++ b/include/linux/can/dev.h
@@ -74,6 +74,7 @@ struct can_priv {
 			    enum can_state *state);
 	int (*do_get_berr_counter)(const struct net_device *dev,
 				   struct can_berr_counter *bec);
+	int (*do_get_auto_tdcv)(const struct net_device *dev, u32 *tdcv);
 
 	unsigned int echo_skb_max;
 	struct sk_buff **echo_skb;
-- 
2.31.1