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SubjectRe: [PATCH] usb: dwc3: gadget: check link trb after free_slot is increased
Hi

On Fri, May 16, 2014 at 05:57:57AM +0800, Zhuang Jin Can wrote:
> In ISOC transfers, when free_slot points to the last TRB (i.e. Link
> TRB), and all queued requests meet Missed Interval Isoc error, busy_slot
> points to trb0.
> busy_slot->trb0
> trb1
> ...
> free_slot->trb31(Link TRB)
>
> After end transfer and receiving the XferNotReady event, trb_left is
> caculated as 1 which is wrong, and no TRB will be primed to the
> endpoint.
>
> The root cause is free_slot is not increased the same way as busy_slot.
> When busy_slot is increased by one, it checks if points to a link TRB
> after increasement, but free_slot checks it before increasement.
> free_slot should behave the same as busy_slot to make the trb_left
> caculation correct.
>
> Signed-off-by: Zhuang Jin Can <jin.can.zhuang@intel.com>
> Signed-off-by: Jiebing Li <jiebing.li@intel.com>
> ---
> drivers/usb/dwc3/gadget.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index 54da8c8..2ebe82b 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -828,10 +828,6 @@ static void dwc3_prepare_one_trb(struct dwc3_ep *dep,
> length, last ? " last" : "",
> chain ? " chain" : "");
>
> - /* Skip the LINK-TRB on ISOC */
> - if (((dep->free_slot & DWC3_TRB_MASK) == DWC3_TRB_NUM - 1) &&
> - usb_endpoint_xfer_isoc(dep->endpoint.desc))
> - dep->free_slot++;
>
> trb = &dep->trb_pool[dep->free_slot & DWC3_TRB_MASK];

I have a feeling this has a negative side effect of letting us use the
link TRB for data transfer... I mean, if we don't increment free_slot
before accessing our trb_pool, we have no way to skip link trb on this
access here.

How did you find the bug ? do you have good instructions on how to
reproduce it ? How did you test the patch and for how long ?

cheers

--
balbi
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