[PATCH 3/4] usb: cdns3: Fix uvc fail when DMA cross 4k boundery since sg enabled

[Frank Li]

Supposed DMA cross 4k bounder problem should be fixed at DEV_VER_V2, but
still met problem when do ISO transfer if sg enabled.

Data pattern likes below when sg enabled, package size is 1k and mult is 2
	[UVC Header(8B) ] [data(3k - 8)] ...

The received data at offset 0xd000 will get 0xc000 data, len 0x70. Error
happen position as below pattern:
	0xd000: wrong
	0xe000: wrong
	0xf000: correct
	0x10000: wrong
	0x11000: wrong
	0x12000: correct
	...

To avoid DMA cross 4k bounder at ISO transfer, reduce burst len according
to start DMA address's alignment.

Fixes: 7733f6c32e36 ("usb: cdns3: Add Cadence USB3 DRD Driver")
Signed-off-by: Frank Li <Frank.Li@xxxxxxx>
---
 drivers/usb/cdns3/cdns3-gadget.c | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/cdns3/cdns3-gadget.c b/drivers/usb/cdns3/cdns3-gadget.c
index 4c6893af22dde..aeca902ab6cc4 100644
--- a/drivers/usb/cdns3/cdns3-gadget.c
+++ b/drivers/usb/cdns3/cdns3-gadget.c
@@ -1120,6 +1120,7 @@ static int cdns3_ep_run_transfer(struct cdns3_endpoint *priv_ep,
 	u32 togle_pcs = 1;
 	int sg_iter = 0;
 	int num_trb_req;
+	int trb_burst;
 	int num_trb;
 	int address;
 	u32 control;
@@ -1243,7 +1244,36 @@ static int cdns3_ep_run_transfer(struct cdns3_endpoint *priv_ep,
 			total_tdl += DIV_ROUND_UP(length,
 					       priv_ep->endpoint.maxpacket);
 
-		trb->length |= cpu_to_le32(TRB_BURST_LEN(priv_ep->trb_burst_size) |
+		trb_burst = priv_ep->trb_burst_size;
+
+		/*
+		 * Supposed DMA cross 4k bounder problem should be fixed at DEV_VER_V2, but still
+		 * met problem when do ISO transfer if sg enabled.
+		 *
+		 * Data pattern likes below when sg enabled, package size is 1k and mult is 2
+		 *       [UVC Header(8B) ] [data(3k - 8)] ...
+		 *
+		 * The received data at offset 0xd000 will get 0xc000 data, len 0x70. Error happen
+		 * as below pattern:
+		 *	0xd000: wrong
+		 *	0xe000: wrong
+		 *	0xf000: correct
+		 *	0x10000: wrong
+		 *	0x11000: wrong
+		 *	0x12000: correct
+		 *	...
+		 *
+		 * But it is still unclear about why error have not happen below 0xd000, it should
+		 * cross 4k bounder. But anyway, the below code can fix this problem.
+		 *
+		 * To avoid DMA cross 4k bounder at ISO transfer, reduce burst len according to 16.
+		 */
+		if (priv_ep->type == USB_ENDPOINT_XFER_ISOC && priv_dev->dev_ver <= DEV_VER_V2)
+			if (ALIGN_DOWN(trb->buffer, SZ_4K) !=
+			    ALIGN_DOWN(trb->buffer + length, SZ_4K))
+				trb_burst = 16;
+
+		trb->length |= cpu_to_le32(TRB_BURST_LEN(trb_burst) |
 					TRB_LEN(length));
 		pcs = priv_ep->pcs ? TRB_CYCLE : 0;
 
-- 
2.34.1