linux-kernel - Re: [PATCH v2] usb: dwc3: core: fix a issue about clear connect state

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Date:   Mon, 19 Oct 2020 22:04:41 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Dejin Zheng <zhengdejin5@...il.com>,
        "balbi@...nel.org" <balbi@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "sergei.shtylyov@...il.com" <sergei.shtylyov@...il.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] usb: dwc3: core: fix a issue about clear connect state

Dejin Zheng wrote:
> According to Synopsys Programming Guide chapter 2.2 Register Resets,
> it cannot reset the DCTL register by setting DCTL.CSFTRST for core soft
> reset, if DWC3 controller as a slave device and stay connected with a usb
> host, then, while rebooting linux, it will fail to reinitialize dwc3 as a
> slave device when the DWC3 controller did not power off.

If you reboot the OS, wouldn't it go through the driver tear-down
sequence and clear the run_stop bit anyway?
However, I can see how this can be an issue.

>  because the
> connection status is incorrect, so we also need to clear DCTL.RUN_STOP
> bit for disabling connect when doing core soft reset.
>
> Fixes: f59dcab176293b6 ("usb: dwc3: core: improve reset sequence")
> Signed-off-by: Dejin Zheng <zhengdejin5@...il.com>
> ---
> v1 -> v2:
> 	* modify some commit messages by Sergei's suggest, Thanks
> 	  very much for Sergei's help!
>
>  drivers/usb/dwc3/core.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> index 2eb34c8b4065..239636c454c2 100644
> --- a/drivers/usb/dwc3/core.c
> +++ b/drivers/usb/dwc3/core.c
> @@ -256,6 +256,7 @@ static int dwc3_core_soft_reset(struct dwc3 *dwc)
>  
>  	reg = dwc3_readl(dwc->regs, DWC3_DCTL);
>  	reg |= DWC3_DCTL_CSFTRST;
> +	reg &= ~DWC3_DCTL_RUN_STOP;
>  	dwc3_writel(dwc->regs, DWC3_DCTL, reg);
>  
>  	/*

There will still be other stale configuration in DCTL if you do this. I
think it's better to reset the other fields of DCTL to the default
(should be all 0s) instead of doing register read-modify-write as what
we're doing here. If not, at least we should use
dwc3_gadget_dctl_write_safe().

Thanks,
Thinh