linux-kernel - Re: [RFT PATCH 1/2] usb: dwc2: Add a 10 ms delay to dwc2_core

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Date:	Sat, 5 Mar 2016 02:52:11 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Douglas Anderson <dianders@...omium.org>, johnyoun@...opsys.com,
	balbi@...nel.org, Heiko Stuebner <heiko@...ech.de>
Cc:	linux@...ewoehner.de, caesar.upstream@...il.com,
	huangtao@...k-chips.com, repk@...plefau.lt, stefan.wahren@...e.com,
	Julius Werner <jwerner@...omium.org>,
	gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFT PATCH 1/2] usb: dwc2: Add a 10 ms delay to dwc2_core_reset()

Hello.

On 03/04/2016 09:23 PM, Douglas Anderson wrote:

>  From testing and trying to make sense of the documentation, it appears
> that a 10 ms delay is needed after resetting the core to make sure that
> everything is stable and consistent.  Let's add it.
>
> In my testing (on rk3288) this allows us to revert commit
> 192cb07f7928 ("usb: dwc2: Fix probe problem on bcm2835").  Though I
> could never reproduce the problems on my board, this might also allow us
> to revert commit bd84f4ae9986 ("usb: dwc2: Add extra delay when forcing
> dr_mode").
>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
>   drivers/usb/dwc2/core.c | 20 ++++++++++++++++++++
>   1 file changed, 20 insertions(+)
>
> diff --git a/drivers/usb/dwc2/core.c b/drivers/usb/dwc2/core.c
> index 5e5a0f135b5a..8710b2d3e770 100644
> --- a/drivers/usb/dwc2/core.c
> +++ b/drivers/usb/dwc2/core.c
> @@ -277,6 +277,26 @@ int dwc2_core_reset(struct dwc2_hsotg *hsotg)
>   		}
>   	} while (!(greset & GRSTCTL_AHBIDLE));
>
> +	/*
> +	 * Sleep for 10-15 ms after the reset to let it finish.
> +	 *
> +	 * It's been confirmed on at least one version of the controller
> +	 * that this is a requirement that this is a requirement in order for

    Saying it once is enough. :-)

[...]

MBR, Sergei