linux-kernel - Re: [PATCH] usb: dwc3: core: Add quirk for enabling AutoRetry feature in the controller

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Date:   Wed, 25 Jul 2018 14:03:25 -0600
From:   Rob Herring <robh@...nel.org>
To:     Anurag Kumar Vulisha <anurag.kumar.vulisha@...inx.com>
Cc:     gregkh@...uxfoundation.org, mark.rutland@....com, balbi@...nel.org,
        v.anuragkumar@...il.com, linux-usb@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: dwc3: core: Add quirk for enabling AutoRetry
 feature in the controller

On Sat, Jul 21, 2018 at 03:58:40PM +0530, Anurag Kumar Vulisha wrote:
> By default when core sees any transaction error(CRC or overflow)
> it replies with terminating retry ACK (Retry=1 and Nump == 0).
> Enabling this Auto Retry feature in controller, on seeing any
> transaction errors makes the core to send an non-terminating ACK
> transaction packet (that is, ACK TP with Retry=1 and Nump != 0).
> Doing so will give controller a chance to recover from the error
> condition.
> 
> Signed-off-by: Anurag Kumar Vulisha <anurag.kumar.vulisha@...inx.com>
> ---
>  Documentation/devicetree/bindings/usb/dwc3.txt |  5 +++++
>  drivers/usb/dwc3/core.c                        | 16 ++++++++++++++++
>  drivers/usb/dwc3/core.h                        |  6 ++++++
>  3 files changed, 27 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/usb/dwc3.txt b/Documentation/devicetree/bindings/usb/dwc3.txt
> index 7f13ebe..2ba2bc2 100644
> --- a/Documentation/devicetree/bindings/usb/dwc3.txt
> +++ b/Documentation/devicetree/bindings/usb/dwc3.txt
> @@ -94,6 +94,11 @@ Optional properties:
>  			this and tx-thr-num-pkt-prd to a valid, non-zero value
>  			1-16 (DWC_usb31 programming guide section 1.2.3) to
>  			enable periodic ESS TX threshold.
> + - snps,enable_auto_retry: Set to enable Auto retry Feature to make the

s/_/-/

> +			controller operating in Host mode on seeing transaction
> +			errors(CRC errors or internal overrun scenerios) on IN
> +			transfers to reply to the device with a non-terminating
> +			retry ACK (i.e, an ACK TP with Retry=1 & Nump != 0)

Seems like the property is unnecessary. When would you not want this 
retry behavior? Why not just enable unconditionally in the driver?

Rob