On Mon, Dec 22, 2014 at 9:34 PM, Felipe Balbi <[email protected]> wrote:
> On Fri, Dec 19, 2014 at 12:40:15PM +0530, Amit Virdi wrote:
>> When scatter gather is used, multiple TRBs are prepared from one DWC3
>> request.
>> Hence, we must set the 'last' flag when the SG is last as well as the TRB is
>> last. The current implementation uses list_is_last to check if the
>> dwc3_request
>> is the last request in the request_list.
>>
>> This doesn't work when SG is used. This is because, when it is the last
>> request,
>> the first TRB preparation (in dwc3_prepare_one_trb) modifies the dwc3_request
>> list's next and prev pointers while moving the URB to req_queued.
>>
>> Hence, list_is_last always return 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]>
>
> you need to Cc stable here and make sure you point out which kernel
> versions this should be backported to. Looks like this sould be:
>
> Cc: <[email protected]> # v3.9+
Okay. I checked the git log. The commit ("usb: dwc3: gadget: fix
scatter gather implementation") was introduced in v3.8-rc5, hence
v3.8, so I need to
Cc: <[email protected]> # v3.8+
>
> Also, how have you tested this ? I need a test case to make sure it
> fails here and this patch really fixes the problem.
>
This bug can be easily reproduced/tested if the gadget driver submits
a urb having number of sg entries mapped to DMA more than 1 on bulk
endpoint. Following is the log snippet once this bug is reproduced:
----
dwc3 dwc3.0: ep2in-bulk: Transfer Not Ready
dwc3 dwc3.0: queing request 24cc5780 to ep2in-bulk length 960002
dwc3 dwc3.0: ep2in-bulk: req 24cc5780 dma 24eb6400 length 2 chain
dwc3 dwc3.0: ep2in-bulk: req 24cc5780 dma 25901800 length 960000
dwc3 dwc3.0: queing request 24cc5000 to ep2in-bulk length 960002
dwc3 dwc3.0: ep2in-bulk: Transfer Not Ready
dwc3 dwc3.0: queing request 24cc5900 to ep2in-bulk length 960002
-----
Without this fix, the hardware never generates "Transfer Complete"
event for the corresponding EP and goes into an unknown state.
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