linux-kernel - [PATCH 3.18 141/183] usb: dwc3: gadget: Fix TRB preparation during SG

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Message-Id: <20150125180816.302390330@linuxfoundation.org>
Date:	Sun, 25 Jan 2015 10:07:43 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Amit Virdi <amit.virdi@...com>,
	Felipe Balbi <balbi@...com>
Subject: [PATCH 3.18 141/183] usb: dwc3: gadget: Fix TRB preparation during SG

3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Amit Virdi <amit.virdi@...com>

commit ec512fb8e5611fed1df2895f90317ce6797d6b32 upstream.

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: e5ba5ec833aa (usb: dwc3: gadget: fix scatter gather implementation)
Signed-off-by: Amit Virdi <amit.virdi@...com>
Signed-off-by: Felipe Balbi <balbi@...com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/usb/dwc3/gadget.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -882,8 +882,7 @@ static void dwc3_prepare_trbs(struct dwc

 				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;
 				}

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