can: gs_usb: add usb quirk for NXP LPC546xx controllers

Introduce a workaround for a NXP chip errata on LPC546xx
controllers (Errata sheet LPC546xx / USB.15).

According to the document corruption can occur when the following
conditions are met:
* A TX (IN) transfer happens after a RX (OUT) transfer.
* The RX (OUT) transfer length is 4 + N * 16 (N >= 0) bytes.

Even though the struct gs_host_frame has a size of 76 bytes for a FD
frame, which does not apply to the above rule, corruption could be
seen.

Adding a dummy byte to break the second condition also on transfer
lengths with 4 + N * 8 bytes reliably circumvents USB transfer data
corruption.

The firmware can now request this quirk by setting
GS_CAN_FEATURE_REQ_USB_QUIRK_LPC546XX.

Link: https://lore.kernel.org/all/20220309124132.291861-17-mkl@pengutronix.deSigned-off-by: Peter Fink <pfink@christ-es.de>
Signed-off-by: Christoph Möhring <cmoehring@christ-es.de>
Signed-off-by: Alexander Schartner <aschartner@christ-es.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/usb/gs_usb.c

@@ -9,6 +9,7 @@
  * Many thanks to all socketcan devs!
  */
 
+#include <linux/bitfield.h>
 #include <linux/ethtool.h>
 #include <linux/init.h>
 #include <linux/module.h>
@@ -100,6 +101,7 @@ struct gs_device_config {
 /* GS_CAN_FEATURE_USER_ID BIT(6) */
 #define GS_CAN_MODE_PAD_PKTS_TO_MAX_PKT_SIZE BIT(7)
 #define GS_CAN_MODE_FD BIT(8)
+/* GS_CAN_FEATURE_REQ_USB_QUIRK_LPC546XX BIT(9) */
 
 struct gs_device_mode {
 	__le32 mode;
@@ -133,6 +135,8 @@ struct gs_identify_mode {
 #define GS_CAN_FEATURE_USER_ID BIT(6)
 #define GS_CAN_FEATURE_PAD_PKTS_TO_MAX_PKT_SIZE BIT(7)
 #define GS_CAN_FEATURE_FD BIT(8)
+#define GS_CAN_FEATURE_REQ_USB_QUIRK_LPC546XX BIT(9)
+#define GS_CAN_FEATURE_MASK GENMASK(9, 0)
 
 struct gs_device_bt_const {
 	__le32 feature;
@@ -156,10 +160,20 @@ struct classic_can {
 	u8 data[8];
 } __packed;
 
+struct classic_can_quirk {
+	u8 data[8];
+	u8 quirk;
+} __packed;
+
 struct canfd {
 	u8 data[64];
 } __packed;
 
+struct canfd_quirk {
+	u8 data[64];
+	u8 quirk;
+} __packed;
+
 struct gs_host_frame {
 	u32 echo_id;
 	__le32 can_id;
@@ -171,7 +185,9 @@ struct gs_host_frame {
 
 	union {
 		DECLARE_FLEX_ARRAY(struct classic_can, classic_can);
+		DECLARE_FLEX_ARRAY(struct classic_can_quirk, classic_can_quirk);
 		DECLARE_FLEX_ARRAY(struct canfd, canfd);
+		DECLARE_FLEX_ARRAY(struct canfd_quirk, canfd_quirk);
 	};
 } __packed;
 /* The GS USB devices make use of the same flags and masks as in
@@ -204,6 +220,7 @@ struct gs_can {
 	struct can_bittiming_const bt_const;
 	unsigned int channel;	/* channel number */
 
+	u32 feature;
 	unsigned int hf_size_tx;
 
 	/* This lock prevents a race condition between xmit and receive. */
@@ -666,8 +683,15 @@ static int gs_can_open(struct net_device *netdev)
 	ctrlmode = dev->can.ctrlmode;
 	if (ctrlmode & CAN_CTRLMODE_FD) {
 		flags |= GS_CAN_MODE_FD;
+
+		if (dev->feature & GS_CAN_FEATURE_REQ_USB_QUIRK_LPC546XX)
+			dev->hf_size_tx = struct_size(hf, canfd_quirk, 1);
+		else
 			dev->hf_size_tx = struct_size(hf, canfd, 1);
 	} else {
+		if (dev->feature & GS_CAN_FEATURE_REQ_USB_QUIRK_LPC546XX)
+			dev->hf_size_tx = struct_size(hf, classic_can_quirk, 1);
+		else
 			dev->hf_size_tx = struct_size(hf, classic_can, 1);
 	}
 
@@ -938,6 +962,7 @@ static struct gs_can *gs_make_candev(unsigned int channel,
 	dev->can.ctrlmode_supported = CAN_CTRLMODE_CC_LEN8_DLC;
 
 	feature = le32_to_cpu(bt_const->feature);
+	dev->feature = FIELD_GET(GS_CAN_FEATURE_MASK, feature);
 	if (feature & GS_CAN_FEATURE_LISTEN_ONLY)
 		dev->can.ctrlmode_supported |= CAN_CTRLMODE_LISTENONLY;