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

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Message-ID: <20201020133805.GA14599@nuc8i5>
Date:   Tue, 20 Oct 2020 21:38:05 +0800
From:   Dejin Zheng <zhengdejin5@...il.com>
To:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>
Cc:     "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>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] usb: dwc3: core: fix a issue about clear connect state

On Mon, Oct 19, 2020 at 10:04:41PM +0000, Thinh Nguyen wrote:
> Dejin Zheng wrote:

Hi Thinh:
> > 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?
Yes, you are right, this is a point worth checking. and I think it might
still be necessary to reset it.

> 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().
>
Thinh, thanks very much for your suggestion, I think it might be better
to reset all areas of DCTL register. I tested it on my SOC platform and
it worked.

BR,
Dejin

> Thanks,
> Thinh
>