From: John Youn <johny...@synopsys.com> The current calculation takes dep->trb_dequeue - dep->trb_enqueue to find the TRB space left.
If you enqueue 1, that results in: (u8) 0 - (u8) 1 = 0xff = 255 TRBs left. This is correct if DWC3_TRB_NUM == 256. If DWC3_TRB_NUM is less than 256 (but still a power of 2) you need to mod the result by DWC3_TRB_NUM. For example the same calculation with DWC3_TRB_NUM = 8, results in: 255 % 6 = 7 TRBs left. Signed-off-by: John Youn <johny...@synopsys.com> Signed-off-by: Felipe Balbi <felipe.ba...@linux.intel.com> --- drivers/usb/dwc3/gadget.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c index d375f86506e9..ad5c06fa9c0c 100644 --- a/drivers/usb/dwc3/gadget.c +++ b/drivers/usb/dwc3/gadget.c @@ -823,6 +823,7 @@ static void dwc3_prepare_one_trb(struct dwc3_ep *dep, static u32 dwc3_calc_trbs_left(struct dwc3_ep *dep) { struct dwc3_trb *tmp; + u8 trbs_left; /* * If enqueue & dequeue are equal than it is either full or empty. @@ -842,7 +843,10 @@ static u32 dwc3_calc_trbs_left(struct dwc3_ep *dep) return DWC3_TRB_NUM - 1; } - return dep->trb_dequeue - dep->trb_enqueue; + trbs_left = dep->trb_dequeue - dep->trb_enqueue; + trbs_left %= DWC3_TRB_NUM; + + return trbs_left; } static void dwc3_prepare_one_trb_sg(struct dwc3_ep *dep, -- 2.8.3 --------------------------------------------------------------------- Intel Finland Oy Registered Address: PL 281, 00181 Helsinki Business Identity Code: 0357606 - 4 Domiciled in Helsinki This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies. -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html