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 <johnyoun@xxxxxxxxxxxx>
---
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 ab22a46..09ced5c 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -859,6 +859,7 @@ 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.
@@ -878,7 +879,10 @@ 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,
--
2.8.2
--
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