Re: [PATCH 1/4] usb: dwc3: gadget: Fix TRB preparation during SG

[Felipe Balbi <balbi@ti.com>]

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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 <amit.virdi@st.com>

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: <stable@vger.kernel.org> # v3.9+

Also, how have you tested this ? I need a test case to make sure it
fails here and this patch really fixes the problem.

> ---
>  drivers/usb/dwc3/gadget.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index f03b136ecfce..0eec2e917994 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -882,8 +882,7 @@ static void dwc3_prepare_trbs(struct dwc3_ep *dep, bool starting)
>  
>  				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;
>  				}
> -- 
> 1.8.0
> 

-- 
balbi

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