usb: dwc3: gadget: Handle 0 xfer length for OUT EP

[Felipe Balbi <balbi@kernel.org>]

Hi,

Tejas Joglekar <tejas.joglekar@synopsys.com> writes:
> For OUT endpoints, zero-length transfers require MaxPacketSize buffer as
> per the DWC_usb3 programming guide 3.30a section 4.2.3.3.
>
> This patch fixes this by explicitly checking zero length
> transfer to correctly pad up to MaxPacketSize.
>
> Signed-off-by: Tejas Joglekar <joglekar@synopsys.com>

do you have tracepoints of the problem?

> ---
>  drivers/usb/dwc3/gadget.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index e2caf9e..f1089ec 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -1069,7 +1069,8 @@ static void dwc3_prepare_one_trb_sg(struct dwc3_ep *dep,
>  		if (sg_is_last(s))
>  			chain = false;
>  
> -		if (rem && usb_endpoint_dir_out(dep->endpoint.desc) && !chain) {
> +		if ((!length || rem) && usb_endpoint_dir_out(dep->endpoint.desc)
> +		    && !chain) {

are you 100% certain we have scatter/gather for a zlp? That doesn't make
sense to me.

> @@ -1114,7 +1115,7 @@ static void dwc3_prepare_one_trb_linear(struct dwc3_ep *dep,
>  	unsigned int maxp = usb_endpoint_maxp(dep->endpoint.desc);
>  	unsigned int rem = length % maxp;
>  
> -	if (rem && usb_endpoint_dir_out(dep->endpoint.desc)) {
> +	if ((!length || rem) && usb_endpoint_dir_out(dep->endpoint.desc)) {

this is already taken care of:

> static void dwc3_prepare_one_trb_linear(struct dwc3_ep *dep,
> 		struct dwc3_request *req)
> {
> 	unsigned int length = req->request.length;
> 	unsigned int maxp = usb_endpoint_maxp(dep->endpoint.desc);
> 	unsigned int rem = length % maxp;
>
> 	if (rem && usb_endpoint_dir_out(dep->endpoint.desc)) {

[...]

> 	} else if (req->request.zero && req->request.length &&
> 		   (IS_ALIGNED(req->request.length, maxp))) {

why isn't this branch triggering for you? Please capture and share
tracepoints exposing the problem

> 		struct dwc3	*dwc = dep->dwc;
> 		struct dwc3_trb	*trb;
>
> 		req->needs_extra_trb = true;
>
> 		/* prepare normal TRB */
> 		dwc3_prepare_one_trb(dep, req, true, 0);
>
> 		/* Now prepare one extra TRB to handle ZLP */
> 		trb = &dep->trb_pool[dep->trb_enqueue];
> 		req->num_trbs++;
> 		__dwc3_prepare_one_trb(dep, trb, dwc->bounce_addr, 0,
> 				false, 1, req->request.stream_id,
> 				req->request.short_not_ok,
> 				req->request.no_interrupt);
> 	} else {
> 		dwc3_prepare_one_trb(dep, req, false, 0);
> 	}
> }