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

["Stéphane Grosjean" <stephane.grosjean@free.fr>]

From: Stéphane Grosjean <s.grosjean@peak-system.fr>

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@peak-system.fr>
---
 drivers/net/can/usb/peak_usb/pcan_usb_fd.c | 14 ++++++++++----
 1 file changed, 10 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 5840623662af..a00ce1f52341 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);
@@ -1266,7 +1272,7 @@ const struct peak_usb_adapter pcan_usb_fd = {
 	.ctrlmode_supported = CAN_CTRLMODE_FD |
 			CAN_CTRLMODE_3_SAMPLES | CAN_CTRLMODE_LISTENONLY |
 			CAN_CTRLMODE_ONE_SHOT | CAN_CTRLMODE_CC_LEN8_DLC |
-			CAN_CTRLMODE_BERR_REPORTING,
+			CAN_CTRLMODE_BERR_REPORTING | CAN_CTRLMODE_LOOPBACK,
 	.clock = {
 		.freq = PCAN_UFD_CRYSTAL_HZ,
 	},
@@ -1343,7 +1349,7 @@ const struct peak_usb_adapter pcan_usb_chip = {
 	.ctrlmode_supported = CAN_CTRLMODE_FD |
 		CAN_CTRLMODE_3_SAMPLES | CAN_CTRLMODE_LISTENONLY |
 		CAN_CTRLMODE_ONE_SHOT | CAN_CTRLMODE_CC_LEN8_DLC |
-		CAN_CTRLMODE_BERR_REPORTING,
+		CAN_CTRLMODE_BERR_REPORTING | CAN_CTRLMODE_LOOPBACK,
 	.clock = {
 		.freq = PCAN_UFD_CRYSTAL_HZ,
 	},
@@ -1420,7 +1426,7 @@ const struct peak_usb_adapter pcan_usb_pro_fd = {
 	.ctrlmode_supported = CAN_CTRLMODE_FD |
 			CAN_CTRLMODE_3_SAMPLES | CAN_CTRLMODE_LISTENONLY |
 			CAN_CTRLMODE_ONE_SHOT | CAN_CTRLMODE_CC_LEN8_DLC |
-			CAN_CTRLMODE_BERR_REPORTING,
+			CAN_CTRLMODE_BERR_REPORTING | CAN_CTRLMODE_LOOPBACK,
 	.clock = {
 		.freq = PCAN_UFD_CRYSTAL_HZ,
 	},
@@ -1497,7 +1503,7 @@ const struct peak_usb_adapter pcan_usb_x6 = {
 	.ctrlmode_supported = CAN_CTRLMODE_FD |
 			CAN_CTRLMODE_3_SAMPLES | CAN_CTRLMODE_LISTENONLY |
 			CAN_CTRLMODE_ONE_SHOT | CAN_CTRLMODE_CC_LEN8_DLC |
-			CAN_CTRLMODE_BERR_REPORTING,
+			CAN_CTRLMODE_BERR_REPORTING | CAN_CTRLMODE_LOOPBACK,
 	.clock = {
 		.freq = PCAN_UFD_CRYSTAL_HZ,
 	},

---
base-commit: baf950233c8efcd3807f771ae5dc3cd6f5326278
change-id: 20260930-peak_usb-canfd-loopback-ffffe0ff9015

Best regards,
--  
Stéphane Grosjean <s.grosjean@peak-system.fr>