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From:   Pawel Laszczak <pawell@cadence.com>
To:     Peter Chen <peter.chen@kernel.org>
CC:     "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
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Subject: RE: [PATCH] usb: cdnsp: fix issue with ZLP - added TD_SIZE = 1
Thread-Topic: [PATCH] usb: cdnsp: fix issue with ZLP - added TD_SIZE = 1
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Date:   Fri, 21 Oct 2022 05:03:25 +0000
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 <20221020132010.GA29690@nchen-desktop>
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>
>
>On 22-10-19 02:07:17, 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@vger.kernel.org>
>> Fixes: 3d82904559f4 ("usb: cdnsp: cdns3 Add main part of Cadence
>> USBSSP DRD Driver")
>> Signed-off-by: Pawel Laszczak <pawell@cadence.com>
>> ---
>>  drivers/usb/cdns3/cdnsp-ring.c | 15 ++++++++-------
>>  1 file changed, 8 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/usb/cdns3/cdnsp-ring.c
>> b/drivers/usb/cdns3/cdnsp-ring.c index 794e413800ae..4809d0e894bb
>> 100644
>> --- a/drivers/usb/cdns3/cdnsp-ring.c
>> +++ b/drivers/usb/cdns3/cdnsp-ring.c
>> @@ -1765,18 +1765,19 @@ static u32 cdnsp_td_remainder(struct
>cdnsp_device *pdev,
>>  			      struct cdnsp_request *preq,
>>  			      bool more_trbs_coming)
>>  {
>> -	u32 maxp, total_packet_count;
>> -
>> -	/* One TRB with a zero-length data packet. */
>> -	if (!more_trbs_coming || (transferred =3D=3D 0 && trb_buff_len =3D=3D =
0) ||
>> -	    trb_buff_len =3D=3D td_total_len)
>> -		return 0;
>> +	u32 maxp, total_packet_count, remainder;
>>
>>  	maxp =3D usb_endpoint_maxp(preq->pep->endpoint.desc);
>>  	total_packet_count =3D DIV_ROUND_UP(td_total_len, maxp);
>>
>>  	/* Queuing functions don't count the current TRB into transferred. */
>> -	return (total_packet_count - ((transferred + trb_buff_len) / maxp));
>> +	remainder =3D (total_packet_count - ((transferred + trb_buff_len) /
>> +maxp));
>> +
>> +	/* Before ZLP driver needs set TD_SIZE=3D1. */
>> +	if (!remainder && more_trbs_coming)
>> +		remainder =3D 1;
>
>Without ZLP, TD_SIZE =3D 0 for the last TRB.
>With ZLP, TD_SIZE =3D 1 for current TRB, and TD_SIZE =3D 0 for the next TR=
B (the
>last zero-length packet) right?

Yes, you have right.

Pawel

>Peter
>
>> +
>> +	return remainder;
>>  }
>>
>>  static int cdnsp_align_td(struct cdnsp_device *pdev,
>> --
>> 2.25.1
>>
>
>--
>
>Thanks,
>Peter Chen

Regards,
Pawel Laszczak