From: Pratham Pratap prathampratap@codeaurora.org

If scatter-gather operation is allowed, a large USB request is split into multiple TRBs. For preparing TRBs for sg list, driver iterates over the list and creates TRB for each sg and mark the chain bit to false for the last sg. The current IOMMU driver is clubbing the list of sgs which shares a page boundary into one and giving it to USB driver. With this the number of sgs mapped it not equal to the the number of sgs passed. Because of this USB driver is not marking the chain bit to false since it couldn't iterate to the last sg. This patch addresses this issue by marking the chain bit to false if it is the last mapped sg.

At a practical level, this patch resolves USB transfer stalls seen with adb on dwc3 based db845c, pixel3 and other qcom hardware after functionfs gadget added scatter-gather support around v4.20.

Credit also to Anurag Kumar Vulisha anurag.kumar.vulisha@xilinx.com who implemented a very similar fix to this issue.

Cc: Felipe Balbi balbi@kernel.org Cc: Yang Fei fei.yang@intel.com Cc: Thinh Nguyen thinhn@synopsys.com Cc: Tejas Joglekar tejas.joglekar@synopsys.com Cc: Andrzej Pietrasiewicz andrzej.p@collabora.com Cc: Jack Pham jackp@codeaurora.org Cc: Todd Kjos tkjos@google.com Cc: Greg KH gregkh@linuxfoundation.org Cc: Linux USB List linux-usb@vger.kernel.org Cc: stable stable@vger.kernel.org #4.20+ Signed-off-by: Pratham Pratap prathampratap@codeaurora.org [jstultz: Slight tweak to remove sg_is_last() usage, reworked commit message, minor comment tweak] Signed-off-by: John Stultz john.stultz@linaro.org --- v2: * Fix typeos and unnecssary parens as suggested by Jack --- drivers/usb/dwc3/gadget.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c index 1b7d2f9cb673..1e00bf2d65a2 100644 --- a/drivers/usb/dwc3/gadget.c +++ b/drivers/usb/dwc3/gadget.c @@ -1071,7 +1071,14 @@ static void dwc3_prepare_one_trb_sg(struct dwc3_ep *dep, unsigned int rem = length % maxp; unsigned chain = true;

- if (sg_is_last(s)) + /* + * IOMMU driver is coalescing the list of sgs which shares a + * page boundary into one and giving it to USB driver. With + * this the number of sgs mapped is not equal to the number of + * sgs passed. So mark the chain bit to false if it isthe last + * mapped sg. + */ + if (i == remaining - 1) chain = false;

if (rem && usb_endpoint_dir_out(dep->endpoint.desc) && !chain) {