Hi,
On 9/5/2018 2:19 AM, Anurag Kumar Vulisha wrote:
> Hi Thinh,
>
> Thanks for spending your time in reviewing this code, please find my comments
> inline
>
>> -----Original Message-----
>> From: Thinh Nguyen [mailto:thinh.ngu...@synopsys.com]
>> Sent: Wednesday, September 05, 2018 11:04 AM
>> To: Anurag Kumar Vulisha <anura...@xilinx.com>; ba...@kernel.org;
>> gre...@linuxfoundation.org
>> Cc: v.anuragku...@gmail.com; linux-usb@vger.kernel.org; linux-
>> ker...@vger.kernel.org
>> Subject: Re: [PATCH v2 1/8] usb: dwc3: Correct the logic for checking TRB
>> full in
>> __dwc3_prepare_one_trb()
>>
>> Hi Anurag,
>>
>> On 8/17/2018 5:25 AM, Anurag Kumar Vulisha wrote:
>>> Availability of TRB's are calculated using dwc3_calc_trbs_left(), which
>>> determines available TRB's based on the HWO bit set in a TRB.
>>>
>>> __dwc3_prepare_one_trb() is called with a TRB which needs to be prepared
>>> for transfer. This __dwc3_prepare_one_trb() calls dwc3_calc_trbs_left()
>>> to determine total available TRBs and set IOC bit if the total available
>>> TRBs are zero. Since the present working TRB(which is passed as an
>>> argument to __dwc3_prepare_one_trb() ) doesn't have HWO bit already set,
>>> there are chances where dwc3_calc_trbs_left() wrongly calculates this
>>> present working TRB as free(since the HWO bit is not yet set). This could
>>> be a problem. This patch correct this issue by setting HWO bit before
>>> calling dwc3_calc_trbs_left()
>>>
>>> Signed-off-by: Anurag Kumar Vulisha <anurag.kumar.vuli...@xilinx.com>
>>> ---
>>> Changes in v2:
>>> 1. Changed the commit message
>>> ---
>>> drivers/usb/dwc3/gadget.c | 4 ++--
>>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
>>> index 69bf137..f73d219 100644
>>> --- a/drivers/usb/dwc3/gadget.c
>>> +++ b/drivers/usb/dwc3/gadget.c
>>> @@ -990,6 +990,8 @@ static void __dwc3_prepare_one_trb(struct dwc3_ep *dep,
>> struct dwc3_trb *trb,
>>> trb->ctrl |= DWC3_TRB_CTRL_ISP_IMI;
>>> }
>>>
>>> + trb->ctrl |= DWC3_TRB_CTRL_HWO;
>>> +
>>> if ((!no_interrupt && !chain) ||
>>> (dwc3_calc_trbs_left(dep) == 0))
>>> trb->ctrl |= DWC3_TRB_CTRL_IOC;
>>> @@ -1000,8 +1002,6 @@ static void __dwc3_prepare_one_trb(struct dwc3_ep
>> *dep, struct dwc3_trb *trb,
>>> if (usb_endpoint_xfer_bulk(dep->endpoint.desc) && dep->stream_capable)
>>> trb->ctrl |= DWC3_TRB_CTRL_SID_SOFN(stream_id);
>>>
>>> - trb->ctrl |= DWC3_TRB_CTRL_HWO;
>>> -
>>> trace_dwc3_prepare_trb(dep, trb);
>>> }
>>>
>> How do you reproduce this issue? We should not set HWO before setting
>> other trb->ctrl bits. Can you provide a driver tracepoint? If there's an
>> issue with the check if ((!no_interrupt && !chain) ||
>> dwc3_calc_trbs_left == 0), then we may need to fix the check there.
>>
> This issue gets triggered very rarely on long runs when dep->trb_enqueue ==
> dep->trb_dequeue.
> In __dwc3_prepare_one_trb() , IOC bit is set when no TRBs are available, so
> that a complete
> event can be generated and TRBs can be cleaned after complete .
> Dwc3_calc_trbs_left() is called
> to determine the available TRBs, which depends on the previous TRB's HWO bit
> set when
> dep->trb_enqueue == dep->trb_dequeue. There are chances where the
> dwc3_calc_trbs_left() wrongly
> returns DWC3_TRB_NUM -1 instead of 0 , even though there are no available
> TRBs. Please
> consider the below example
>
> 1. Consider a TRB passed to __dwc3_prepare_one_trb() is the last available
> TRB in the pool.
> 2. __dwc3_prepare_one_trb() calls dwc3_ep_inc_enq() which increments the
> dep->trb_enqueue
> before preparing the TRB and since the current TRB is the last available,
> incrementing
> dep->enqueue will make dep->enqueue == dep->dequeue
> 3. IOC bit is set by __dwc3_prepare_one_trb() only when
> dwc3_calc_trbs_left() returns 0 (empty TRBs)
> 4. Since dep->enqueue == dep->dequeue and the previous TRB(the one which we
> are working)
> doesn't yet has the HWO bit set, dwc3_calc_trbs_left() returns
> DWC3_TRB_NUM -1 instead of
> zero (Though there are no available TRBs)
> 5. Since Dwc3_calc_trbs_left() returns non-zero value, IOC bit is not set in
> __dwc3_prepare_one_trb()
> for the last TRB and no complete event is generated. Because of this no
> further TRBs are queued.
>
> To avoid the above mentioned issue, I moved the code logic for setting HWO
> bit before setting IOC bit.
> I agree that HWO bit should always be set at the last, but I didn't find any
> better logic for fixing this.
> Please suggest if any better way to handle this situation.
>
I haven't tested it, but you can try this:
diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index d7a327eaee12..37171d46390b 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -924,8 +924,6 @@ static void __dwc3_prepare_one_trb(struct dwc3_ep
*dep, struct dwc3_trb *trb,
struct usb_gadget *gadget = &dwc->gadget;
enum usb_device_speed speed = gadget->speed;
- dwc3_ep_inc_enq(dep);
-
trb->size = DWC3_TRB_SIZE_LENGTH(length);
trb->bpl = lower_32_bits(dma);
trb->bph = upper_32_bits(dma);
@@ -1004,7 +1002,7 @@ static void __dwc3_prepare_one_trb(struct dwc3_ep
*dep, struct dwc3_trb *trb,
}
if ((!no_interrupt && !chain) ||
- (dwc3_calc_trbs_left(dep) == 0))
+ (dwc3_calc_trbs_left(dep) == 1))
trb->ctrl |= DWC3_TRB_CTRL_IOC;
if (chain)
@@ -1013,6 +1011,8 @@ static void __dwc3_prepare_one_trb(struct dwc3_ep
*dep, struct dwc3_trb *trb,
if (usb_endpoint_xfer_bulk(dep->endpoint.desc) &&
dep->stream_capable)
trb->ctrl |= DWC3_TRB_CTRL_SID_SOFN(stream_id);
+ dwc3_ep_inc_enq(dep);
+
trb->ctrl |= DWC3_TRB_CTRL_HWO;
trace_dwc3_prepare_trb(dep, trb);
BR,
Thinh
