[PATCH] usb: dwc2: gadget: Don't write invalid mapped sg entries into dma_desc with iommu enabled

[Peng Hongchi]

When using dma_map_sg() to map the scatterlist with iommu enabled,
the entries in the scatterlist can be mergerd into less but longer
entries in the function __finalise_sg(). So that the number of
valid mapped entries is actually smaller than ureq->num_reqs,and
there are still some invalid entries in the scatterlist with
dma_addr=0xffffffff and len=0. Writing these invalid sg entries
into the dma_desc can cause a data transmission error.

The function dma_map_sg() returns the number of valid map entries
and the return value is assigned to usb_request::num_mapped_sgs in
function usb_gadget_map_request_by_dev(). So that just write valid
mapped entries into dma_desc according to the usb_request::num_mapped_sgs,
and set the IOC bit if it's the last valid mapped entry.

This patch poses no risk to no-iommu situation, cause
ureq->num_mapped_sgs equals ureq->num_sgs while using dma_direct_map_sg()
to map the scatterlist whith iommu disabled.

Signed-off-by: Peng Hongchi <hongchi.peng@xxxxxxxxxxxx>
---
 drivers/usb/dwc2/gadget.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/dwc2/gadget.c b/drivers/usb/dwc2/gadget.c
index 74ac79abd8f3..e7bf9cc635be 100644
--- a/drivers/usb/dwc2/gadget.c
+++ b/drivers/usb/dwc2/gadget.c
@@ -885,10 +885,10 @@ static void dwc2_gadget_config_nonisoc_xfer_ddma(struct dwc2_hsotg_ep *hs_ep,
 	}
 
 	/* DMA sg buffer */
-	for_each_sg(ureq->sg, sg, ureq->num_sgs, i) {
+	for_each_sg(ureq->sg, sg, ureq->num_mapped_sgs, i) {
 		dwc2_gadget_fill_nonisoc_xfer_ddma_one(hs_ep, &desc,
 			sg_dma_address(sg) + sg->offset, sg_dma_len(sg),
-			sg_is_last(sg));
+			(i == (ureq->num_mapped_sgs - 1)));
 		desc_count += hs_ep->desc_count;
 	}
 
-- 
2.34.1