linux-kernel - [RFC][PATCH 1/2] usb: dwc3: gadget: Check for IOC/LST bit in both event->status and TRB->ctrl fields

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Date:   Wed, 22 Jan 2020 22:26:44 +0000
From:   John Stultz <john.stultz@...aro.org>
To:     lkml <linux-kernel@...r.kernel.org>
Cc:     Anurag Kumar Vulisha <anurag.kumar.vulisha@...inx.com>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Yang Fei <fei.yang@...el.com>,
        Thinh Nguyen <thinhn@...opsys.com>,
        Tejas Joglekar <tejas.joglekar@...opsys.com>,
        Andrzej Pietrasiewicz <andrzej.p@...labora.com>,
        Jack Pham <jackp@...eaurora.org>, Todd Kjos <tkjos@...gle.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Linux USB List <linux-usb@...r.kernel.org>,
        stable <stable@...r.kernel.org>,
        John Stultz <john.stultz@...aro.org>
Subject: [RFC][PATCH 1/2] usb: dwc3: gadget: Check for IOC/LST bit in both event->status and TRB->ctrl fields

From: Anurag Kumar Vulisha <anurag.kumar.vulisha@...inx.com>

The present code in dwc3_gadget_ep_reclaim_completed_trb() will check
for IOC/LST bit in the event->status and returns if IOC/LST bit is
set. This logic doesn't work if multiple TRBs are queued per
request and the IOC/LST bit is set on the last TRB of that request.
Consider an example where a queued request has multiple queued TRBs
and IOC/LST bit is set only for the last TRB. In this case, the Core
generates XferComplete/XferInProgress events only for the last TRB
(since IOC/LST are set only for the last TRB). As per the logic in
dwc3_gadget_ep_reclaim_completed_trb() event->status is checked for
IOC/LST bit and returns on the first TRB. This makes the remaining
TRBs left unhandled.
To aviod this, changed the code to check for IOC/LST bits in both
event->status & TRB->ctrl. This patch does the same.

At a practical level, this patch resolves USB transfer stalls seen
with adb on dwc3 based HiKey960 after functionfs gadget added
scatter-gather support around v4.20.

Cc: Felipe Balbi <felipe.balbi@...ux.intel.com>
Cc: Yang Fei <fei.yang@...el.com>
Cc: Thinh Nguyen <thinhn@...opsys.com>
Cc: Tejas Joglekar <tejas.joglekar@...opsys.com>
Cc: Andrzej Pietrasiewicz <andrzej.p@...labora.com>
Cc: Jack Pham <jackp@...eaurora.org>
Cc: Todd Kjos <tkjos@...gle.com>
Cc: Greg KH <gregkh@...uxfoundation.org>
Cc: Linux USB List <linux-usb@...r.kernel.org>
Cc: stable <stable@...r.kernel.org>
Tested-by: Tejas Joglekar <tejas.joglekar@...opsys.com>
Reviewed-by: Thinh Nguyen <thinhn@...opsys.com>
Signed-off-by: Anurag Kumar Vulisha <anurag.kumar.vulisha@...inx.com>
[jstultz: forward ported to mainline, added note to commit log]
Signed-off-by: John Stultz <john.stultz@...aro.org>
---
 drivers/usb/dwc3/gadget.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 154f3f3e8cff..1edce3bbb55c 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -2420,7 +2420,12 @@ static int dwc3_gadget_ep_reclaim_completed_trb(struct dwc3_ep *dep,
 	if (event->status & DEPEVT_STATUS_SHORT && !chain)
 		return 1;

-	if (event->status & DEPEVT_STATUS_IOC)
+	if ((event->status & DEPEVT_STATUS_IOC) &&
+	    (trb->ctrl & DWC3_TRB_CTRL_IOC))
+		return 1;
+
+	if ((event->status & DEPEVT_STATUS_LST) &&
+	    (trb->ctrl & DWC3_TRB_CTRL_LST))
 		return 1;

 	return 0;
-- 
2.17.1