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

[Pawel Laszczak]

>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 
  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

>
>Peter
>
>
>
>>
>> 2.
>>         TRB1 - length >1 and we don't except ZLP
>>
>> In this case TD_SIZE should be set to 0 for TRB1 and function returns 0,
>more_trbs_comming for TRB1 will be set to 0.
>>
>> 3 More TRBs without ZLP:
>>         e.g.
>>         TRB1  -  length > 0,  more_trbs_comming = 1 - TD_SIZE  > 0
>>         TRB2 -  length > 0, more_trbs_comming = 1  - TD_SIZE > 0
>>         TRB3 - length >= 0, more_trbs_comming = 0 -  TD_SIZE  = 0
>>
>> Pawel
>>
>> >
>> >Peter
>> >
>> >> e.g.
>> >>
>> >> TD -> TRB1  transfer_length = 64KB, TD_SIZE =0
>> >>           TRB2 transfer_length =0, TD_SIZE = 0  - controller will
>> >>                  ignore this transfer and stop transfer on previous
>> >> one
>> >>
>> >> TD -> TRB1  transfer_length = 64KB, TD_SIZE =1
>> >>           TRB2 transfer_length =0, TD_SIZE = 0  - controller will
>> >>                  execute this trb and send ZLP
>> >>
>> >> As you noticed previously, previous fix for last TRB returned
>> >> TD_SIZE = 1 in some cases.
>> >> Previous fix was working correct but was not compliance with
>> >> controller specification.
>> >>
>> >> >
>> >> >>
>> >> >>   maxp = usb_endpoint_maxp(preq->pep->endpoint.desc);
>> >> >>   total_packet_count = DIV_ROUND_UP(td_total_len, maxp);
>> >> >> --
>> >> >> 2.25.1
>> >> >>
>> >> >
>> >> >--
>> >> >
>> >>
>> >> Thanks,
>> >> Pawel Laszczak
>> >
>> >--
>> >
>> >Thanks,
>> >Peter Chen
>>
>> Regards,
>> Pawel Laszczak