When scatter gather (SG) is used, multiple TRBs are prepared from one DWC3
request (dwc3_request). So while preparing TRBs, the 'last' flag should be set
only when it is the last TRB being prepared from the last dwc3_request entry.
The current implementation uses list_is_last to check if the dwc3_request is the
last entry from the request_list. However, list_is_last returns false for the
last entry too. This is because, while preparing the first TRB from a request,
the function dwc3_prepare_one_trb modifies the request's next and prev pointers
while moving the URB to req_queued. Hence, list_is_last always returns false no
matter what.
The correct way is not to access the modified pointers of dwc3_request but to
use list_empty macro instead.
Fixes: e5ba5ec833aa4a76980b512d6a6779643516b850 ("usb: dwc3: gadget: fix scatter
gather implementation"
Signed-off-by: Amit Virdi <[email protected]>
Cc: <[email protected]> # v3.9+
---
drivers/usb/dwc3/gadget.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 4e2593993fae..cb8939134c32 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -879,8 +879,7 @@ static void dwc3_prepare_trbs(struct dwc3_ep *dep, bool
starting)
if (i == (request->num_mapped_sgs - 1) ||
sg_is_last(s)) {
- if (list_is_last(&req->list,
- &dep->request_list))
+ if (list_empty(&dep->request_list))
last_one = true;
chain = false;
}
--
1.8.0
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