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usb: dwc3: gadget: Account for max size in TRB space 

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@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
This commit is contained in:
John Youn 2016-05-19 17:26:12 -07:00 committed by Felipe Balbi
parent 89bc856e5a
commit 32db3d9437
1 changed files with 5 additions and 1 deletions
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6
drivers/usb/dwc3/gadget.c
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@ -845,6 +845,7 @@ 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.
@ -864,7 +865,10 @@ 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,