Re: [PATCH v2] usb: cdnsp: fix issue with ZLP - added TD_SIZE = 1

[Peter Chen]

On Thu, Nov 10, 2022 at 1:38 PM Pawel Laszczak <pawell@xxxxxxxxxxx> wrote:
>
> >On Mon, Nov 7, 2022 at 1:39 PM Pawel Laszczak <pawell@xxxxxxxxxxx>
> >wrote:
> >>
> >> >
> >> >
> >> >On 22-10-27 08:46:17, Pawel Laszczak wrote:
> >> >>
> >> >> >
> >> >> >On 22-10-24 10:04:35, Pawel Laszczak wrote:
> >> >> >> Patch modifies the TD_SIZE in TRB before ZLP TRB.
> >> >> >> The TD_SIZE in TRB before ZLP TRB must be set to 1 to force
> >> >> >> processing ZLP TRB by controller.
> >> >> >>
> >> >> >> cc: <stable@xxxxxxxxxxxxxxx>
> >> >> >> Fixes: 3d82904559f4 ("usb: cdnsp: cdns3 Add main part of Cadence
> >> >> >> USBSSP DRD Driver")
> >> >> >> Signed-off-by: Pawel Laszczak <pawell@xxxxxxxxxxx>
> >> >> >>
> >> >> >> ---
> >> >> >> Changelog:
> >> >> >> v2:
> >> >> >> - returned value for last TRB must be 0
> >> >> >>
> >> >> >>  drivers/usb/cdns3/cdnsp-ring.c | 7 ++++++-
> >> >> >>  1 file changed, 6 insertions(+), 1 deletion(-)
> >> >> >>
> >> >> >> diff --git a/drivers/usb/cdns3/cdnsp-ring.c
> >> >> >> b/drivers/usb/cdns3/cdnsp-ring.c index
> >> >> >> 04dfcaa08dc4..aa79bce89d8a
> >> >> >> 100644
> >> >> >> --- a/drivers/usb/cdns3/cdnsp-ring.c
> >> >> >> +++ b/drivers/usb/cdns3/cdnsp-ring.c
> >> >> >> @@ -1769,8 +1769,13 @@ static u32 cdnsp_td_remainder(struct
> >> >> >> cdnsp_device *pdev,
> >> >> >>
> >> >> >>   /* One TRB with a zero-length data packet. */
> >> >> >>   if (!more_trbs_coming || (transferred == 0 && trb_buff_len == 0) ||
> >> >> >> -     trb_buff_len == td_total_len)
> >> >> >> +     trb_buff_len == td_total_len) {
> >> >> >> +         /* Before ZLP driver needs set TD_SIZE=1. */
> >> >> >> +         if (more_trbs_coming)
> >> >> >> +                 return 1;
> >> >> >> +
> >> >> >>           return 0;
> >> >> >> + }
> >> >> >
> >> >> >Does that fix the issue you want at bulk transfer, which has
> >> >> >zero-length packet at the last packet? It seems not align with
> >> >> >your previous
> >> >fix.
> >> >> >Would you mind explaining more?
> >> >>
> >> >> Value returned by function cdnsp_td_remainder is used as TD_SIZE in
> >> >> TRB.
> >> >>
> >> >> The last TRB in TD should have TD_SIZE=0, so trb for ZLP should
> >> >> have set also TD_SIZE=0. If driver set TD_SIZE=0 on before the last
> >> >> one TRB then the controller stops the transfer and ignore trb for ZLP
> >packet.
> >> >>
> >> >> To fix this, the driver in such case must set TD_SIZE = 1 before
> >> >> the last TRB.
> >> >
> >> >       if (!more_trbs_coming || (transferred == 0 && trb_buff_len == 0) ||
> >> > -         trb_buff_len == td_total_len)
> >> > +         trb_buff_len == td_total_len) {
> >> > +             /* Before ZLP driver needs set TD_SIZE=1. */
> >> > +             if (more_trbs_coming)
> >> > +                     return 1;
> >> > +
> >> >               return 0;
> >> > +     }
> >> >
> >> >How your above fix could return TD_SIZE as 1 for last non-ZLP TRB?
> >> >Which conditions are satisfied?
> >>
> >> For last non-ZLP TRB TD_SIZE should be 0 or 1.
> >>
> >> We have three casess:
> >> 1.
> >>         TRB1 - length > 1
> >>         TRb2 - ZLP
> >>
> >> In this case TRB1 should have set TD_SIZE = 1. In this case the condition
> >>         if (more_trbs_coming)
> >>                 return 1;
> >>
> >> returns TD_SIZE=1. In this case more_trb_comming for TRB1 is 1 and for
> >> TRB2 is 0
> >>
> >
> >This one is my question. How below condition is true for your case 1:
> >
> > if (!more_trbs_coming || (transferred == 0 && trb_buff_len == 0) ||
> >          trb_buff_len == td_total_len)
>
> For TRB1:
>    more_trbs_coming = true
>    transferred == 0 && trb_buff_len == 0  - false - it does not matter in this case
>    trb_buff_len == td_total_len - true

Why trb_buff_len equals to td_total_length? Considering the bulk
transfer with request length
larger than 64KB.

Peter

>   so whole condition is true.
>
>   Because more_trb_comming = true so:
>              if (more_trbs_coming)
>                         return 1;
> returns TD_SIZE = 1
>
> For TRB2 - ZLP:
>    more_trbs_coming = false
>    transferred == 0 && trb_buff_len == 0  - false - it does not matter in this case
>    trb_buff_len == td_total_len - true
>
>   Because more_trb_comming = false so function returns TD_SIZE = 0  for last ZLP trb.
>
> Pawel