linux-kernel - [PATCH v2] usb: dwc3: gadget: Check for IOC/LST bit in TRB->ctrl fields

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Message-Id: <20200127193046.110258-1-john.stultz@linaro.org>
Date:   Mon, 27 Jan 2020 19:30:46 +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 <balbi@...nel.org>, 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: [PATCH v2] usb: dwc3: gadget: Check for IOC/LST bit in TRB->ctrl fields

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

The current 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 leaves the remaining TRBs left unhandled.

Similarly, if the gadget function enqueues an unaligned request
with sglist already in it, it should fail the same way, since we
will append another TRB to something that already uses more than
one TRB.

To aviod this, this patch changes the code to check for IOC/LST
bits in TRB->ctrl instead.

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 <balbi@...nel.org>
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, reworded commit log, reworked
 to only check trb->ctrl as suggested by Felipe]
Signed-off-by: John Stultz <john.stultz@...aro.org>
---
v2:
* Rework to only check trb->ctrl as suggested by Felipe
* Reword the commit message to include more of Felipe's assessment
---
 drivers/usb/dwc3/gadget.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 154f3f3e8cff..9a085eee1ae3 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -2420,7 +2420,8 @@ 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 ((trb->ctrl & DWC3_TRB_CTRL_IOC) ||
+	    (trb->ctrl & DWC3_TRB_CTRL_LST))
 		return 1;

 	return 0;
-- 
2.17.1