linux-kernel - Re: [PATCH v3 1/8] usb: dwc3: Correct the logic for checking TRB full in __dwc3_prepare_one

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Message-ID: <30102591E157244384E984126FC3CB4F544AD8B3@us01wembx1.internal.synopsys.com>
Date:   Fri, 7 Sep 2018 23:28:57 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Anurag Kumar Vulisha <anurag.kumar.vulisha@...inx.com>,
        "balbi@...nel.org" <balbi@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Thinh.Nguyen@...opsys.com" <Thinh.Nguyen@...opsys.com>,
        "v.anuragkumar@...il.com" <v.anuragkumar@...il.com>
Subject: Re: [PATCH v3 1/8] usb: dwc3: Correct the logic for checking TRB
 full in __dwc3_prepare_one_trb()

Hi Anurag,

On 9/7/2018 6:14 AM, Anurag Kumar Vulisha wrote:
> Availability of TRB's are calculated using dwc3_calc_trbs_left(), which
> determines available TRB's based on the HWO bit set in a TRB.
>
> __dwc3_prepare_one_trb() is called with a TRB which needs to be prepared
> for transfer. This __dwc3_prepare_one_trb() calls dwc3_calc_trbs_left()
> to determine total available TRBs and set IOC bit if the total available
> TRBs are zero. Since the present working TRB(which is passed as an
> argument to __dwc3_prepare_one_trb() )  doesn't have HWO bit already set,
> there are chances where dwc3_calc_trbs_left() wrongly calculates this
> present working TRB as free(since the HWO bit is not yet set). This could
> be a problem. This patch correct this issue by setting HWO bit before
> calling dwc3_calc_trbs_left()

Please revise your commit message to reflect your new change.

>
> Signed-off-by: Anurag Kumar Vulisha <anurag.kumar.vulisha@...inx.com>
> Reviewed-by: Thinh Nguyen <thinhn@...opsys.com>
> ---
>  Changes in v3:
> 	1. Corrected the logic for setting HWO bit as suggested by "Thinh Nguyen"
>
>  Changes in v2:
> 	1. Changed the commit message
> ---
>  drivers/usb/dwc3/gadget.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index 032ea7d..8a1622b 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -911,8 +911,6 @@ static void __dwc3_prepare_one_trb(struct dwc3_ep *dep, struct dwc3_trb *trb,
>  	struct usb_gadget	*gadget = &dwc->gadget;
>  	enum usb_device_speed	speed = gadget->speed;
>  
> -	dwc3_ep_inc_enq(dep);
> -
>  	trb->size = DWC3_TRB_SIZE_LENGTH(length);
>  	trb->bpl = lower_32_bits(dma);
>  	trb->bph = upper_32_bits(dma);
> @@ -991,7 +989,7 @@ static void __dwc3_prepare_one_trb(struct dwc3_ep *dep, struct dwc3_trb *trb,
>  	}
>  
>  	if ((!no_interrupt && !chain) ||
> -			(dwc3_calc_trbs_left(dep) == 0))
> +			(dwc3_calc_trbs_left(dep) == 1))
>  		trb->ctrl |= DWC3_TRB_CTRL_IOC;
>  
>  	if (chain)
> @@ -1002,6 +1000,8 @@ static void __dwc3_prepare_one_trb(struct dwc3_ep *dep, struct dwc3_trb *trb,
>  
>  	trb->ctrl |= DWC3_TRB_CTRL_HWO;
>  
> +	dwc3_ep_inc_enq(dep);
> +
>  	trace_dwc3_prepare_trb(dep, trb);
>  }
>  

BR,
Thinh