[PATCH v2] can: peak_usb: Add support of loopback mode to the PCAN-USB FD family

[Stéphane Grosjean]

From: Stéphane Grosjean <s.grosjean@xxxxxxxxxxxxxx>

This commit adds loopback mode support for all PEAK-System USB-to-CAN FD
interfaces.

The implementation follows the same approach as the peak_pciefd driver.
The only difference is local echo handling: on USB devices, transmit
confirmations are provided through USB write acknowledgments rather than
through the reception of a controller-generated loopback frame.

Signed-off-by: Stéphane Grosjean <s.grosjean@xxxxxxxxxxxxxx>
---
Changes in v2:
- Rebase on top of the CAN_CTRLMODE sorting patch requested by
  Marc Kleine-Budde.
- Keep CAN_CTRLMODE flags sorted by value.
- Link to v1: https://patch.msgid.link/20260930-peak_usb-canfd-loopback-v1-1-fdcb87611fc6@xxxxxxxxxxxxxx

To: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>
To: Vincent Mailhol <mailhol@xxxxxxxxxx>
Cc: linux-can@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 drivers/net/can/usb/peak_usb/pcan_usb_fd.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/drivers/net/can/usb/peak_usb/pcan_usb_fd.c b/drivers/net/can/usb/peak_usb/pcan_usb_fd.c
index 9081f30e3d35..59debe009f92 100644
--- a/drivers/net/can/usb/peak_usb/pcan_usb_fd.c
+++ b/drivers/net/can/usb/peak_usb/pcan_usb_fd.c
@@ -934,6 +934,12 @@ static int pcan_usb_fd_encode_msg(struct peak_usb_device *dev,
 	if (dev->can.ctrlmode & CAN_CTRLMODE_ONE_SHOT)
 		tx_msg_flags |= PUCAN_MSG_SINGLE_SHOT;
 
+	/* Request controller loopback and mark the frame as self-received,
+	 * matching the behavior of the peak_pciefd driver.
+	 */
+	if (dev->can.ctrlmode & CAN_CTRLMODE_LOOPBACK)
+		tx_msg_flags |= PUCAN_MSG_LOOPED_BACK | PUCAN_MSG_SELF_RECEIVE;
+
 	tx_msg->flags = cpu_to_le16(tx_msg_flags);
 	tx_msg->channel_dlc = PUCAN_MSG_CHANNEL_DLC(dev->ctrl_idx, dlc);
 	memcpy(tx_msg->d, cfd->data, cfd->len);
@@ -1263,7 +1269,8 @@ const struct peak_usb_adapter pcan_usb_fd = {
 	.name = "PCAN-USB FD",
 	.device_id = PCAN_USBFD_PRODUCT_ID,
 	.ctrl_count = PCAN_USBFD_CHANNEL_COUNT,
-	.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY |
+	.ctrlmode_supported = CAN_CTRLMODE_LOOPBACK |
+			      CAN_CTRLMODE_LISTENONLY |
 			      CAN_CTRLMODE_3_SAMPLES |
 			      CAN_CTRLMODE_ONE_SHOT |
 			      CAN_CTRLMODE_BERR_REPORTING |
@@ -1342,7 +1349,8 @@ const struct peak_usb_adapter pcan_usb_chip = {
 	.name = "PCAN-Chip USB",
 	.device_id = PCAN_USBCHIP_PRODUCT_ID,
 	.ctrl_count = PCAN_USBFD_CHANNEL_COUNT,
-	.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY |
+	.ctrlmode_supported = CAN_CTRLMODE_LOOPBACK |
+			      CAN_CTRLMODE_LISTENONLY |
 			      CAN_CTRLMODE_3_SAMPLES |
 			      CAN_CTRLMODE_ONE_SHOT |
 			      CAN_CTRLMODE_BERR_REPORTING |
@@ -1421,7 +1429,8 @@ const struct peak_usb_adapter pcan_usb_pro_fd = {
 	.name = "PCAN-USB Pro FD",
 	.device_id = PCAN_USBPROFD_PRODUCT_ID,
 	.ctrl_count = PCAN_USBPROFD_CHANNEL_COUNT,
-	.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY |
+	.ctrlmode_supported = CAN_CTRLMODE_LOOPBACK |
+			      CAN_CTRLMODE_LISTENONLY |
 			      CAN_CTRLMODE_3_SAMPLES |
 			      CAN_CTRLMODE_ONE_SHOT |
 			      CAN_CTRLMODE_BERR_REPORTING |
@@ -1500,7 +1509,8 @@ const struct peak_usb_adapter pcan_usb_x6 = {
 	.name = "PCAN-USB X6",
 	.device_id = PCAN_USBX6_PRODUCT_ID,
 	.ctrl_count = PCAN_USBPROFD_CHANNEL_COUNT,
-	.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY |
+	.ctrlmode_supported = CAN_CTRLMODE_LOOPBACK |
+			      CAN_CTRLMODE_LISTENONLY |
 			      CAN_CTRLMODE_3_SAMPLES |
 			      CAN_CTRLMODE_ONE_SHOT |
 			      CAN_CTRLMODE_BERR_REPORTING |
-- 
2.43.0

Best regards,
---
Stéphane Grosjean <s.grosjean@xxxxxxxxxxxxxx>