linux-kernel - Re: [PATCH] usb: cdnsp: fix issue with ZLP

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Message-ID: <20221020132010.GA29690@nchen-desktop>
Date:   Thu, 20 Oct 2022 21:20:10 +0800
From:   Peter Chen <peter.chen@...nel.org>
To:     Pawel Laszczak <pawell@...ence.com>
Cc:     gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] usb: cdnsp: fix issue with ZLP - added TD_SIZE = 1

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@...r.kernel.org>
> Fixes: 3d82904559f4 ("usb: cdnsp: cdns3 Add main part of Cadence USBSSP DRD Driver")
> Signed-off-by: Pawel Laszczak <pawell@...ence.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 == 0 && trb_buff_len == 0) ||
> -	    trb_buff_len == td_total_len)
> -		return 0;
> +	u32 maxp, total_packet_count, remainder;
>  
>  	maxp = usb_endpoint_maxp(preq->pep->endpoint.desc);
>  	total_packet_count = 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 = (total_packet_count - ((transferred + trb_buff_len) / maxp));
> +
> +	/* Before ZLP driver needs set TD_SIZE=1. */
> +	if (!remainder && more_trbs_coming)
> +		remainder = 1;

Without ZLP, TD_SIZE = 0 for the last TRB.
With ZLP, TD_SIZE = 1 for current TRB, and TD_SIZE = 0 for the next TRB
(the last zero-length packet) right?

Peter

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

-- 

Thanks,
Peter Chen