Hi, John Youn <John.Youn@xxxxxxxxxxxx> writes: > On 8/25/2016 12:38 AM, Felipe Balbi wrote: >> We need to decrement in both cases (enq > deq and >> enq < deq) >> >> Signed-off-by: Felipe Balbi <felipe.balbi@xxxxxxxxxxxxxxx> >> --- >> drivers/usb/dwc3/gadget.c | 5 +---- >> 1 file changed, 1 insertion(+), 4 deletions(-) >> >> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c >> index 594e82595634..e4ef9ed1a143 100644 >> --- a/drivers/usb/dwc3/gadget.c >> +++ b/drivers/usb/dwc3/gadget.c >> @@ -884,12 +884,9 @@ static u32 dwc3_calc_trbs_left(struct dwc3_ep *dep) >> return DWC3_TRB_NUM - 1; >> } >> >> - trbs_left = dep->trb_dequeue - dep->trb_enqueue; >> + trbs_left = dep->trb_dequeue - dep->trb_enqueue - 1; >> trbs_left &= (DWC3_TRB_NUM - 1); >> >> - if (dep->trb_dequeue < dep->trb_enqueue) >> - trbs_left--; >> - >> return trbs_left; >> } >> >> > > Hi Felipe, > > I don't think that's right. > > The decrement is accounting for the fact that the link TRB is taking > up one of the free spots. That is only the case when the deq < enq. > > See the examples below to illustrate this > > > Example 1 (DWC3_TRB_NUM = 8): After the initial state of the ring, > queue on TRB. > > 0: TRB <- deq > 1: empty <- enq > 2: empty > 3: empty > 4: empty > 5: empty > 6: empty > 7: LINK TRB > > enq=1, deq=0 > > num_free => > (deq - enq) % DWC3_TRB_NUM => > (0 - 1) % 8 => > 0xffffffff % 8 => > 7 slots free > > One of the free slots is take up by link trb so decrement by 1: > > 7 - 1 => 6 slots free > > > Example 2 (DWC3_TRB_NUM = 8): The enqueue pointer has wrapped around > and started enqueue from the beginning of the ring again, but the > dequeue pointer hasn't wrapped yet. > > 0: TRB > 1: empty <- enq > 2: empty > 3: empty > 4: TRB <- deq > 5: TRB > 6: TRB > 7: LINK TRB > > enq = 1, deq = 4 > > num_free => > (deq - enq) % DWC3_TRB_NUM => > (4 - 1) % 8 => > 3 slots free > > No need to decrement by 1. Argh, you're right. Can you send a revert patch. I ended up sending this to Greg. Sorry. -- balbi
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