linux-kernel - RE: [RESEND][PATCH v3 1/2] usb: dwc3: Add avoiding vbus glitch happen during xhci reset

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Date:   Thu, 6 Jun 2019 08:20:03 +0000
From:   Ran Wang <ran.wang_1@....com>
To:     Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Felipe Balbi <balbi@...nel.org>, Yang Li <pku.leo@...il.com>
CC:     "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [RESEND][PATCH v3 1/2] usb: dwc3: Add avoiding vbus glitch happen
 during xhci reset

Hi Sergei,

On Thursday, June 06, 2019 16:17 Sergei Shtylyov wrote:
> 
> Hello!
> 
> On 06.06.2019 5:54, Ran Wang wrote:
> 
> > When DWC3 is set to host mode by programming register DWC3_GCTL, VBUS
> > (or its control signal) will turn on immediately on related Root Hub
> > ports. Then the VBUS will be de-asserted for a little while during
> > xhci reset (conducted by xhci driver) for a little while and back to normal.
> >
> > This VBUS glitch might cause some USB devices emuration fail if kernel
> 
>     Enumeration. :-)

Thanks, will correct it in next version
 
Regards,
Ran

> > boot with them connected. One SW workaround which can fix this is to
> > program all PORTSC[PP] to 0 to turn off VBUS immediately after setting
> > host mode in DWC3 driver(per signal measurement result, it will be too
> > late to do it in xhci-plat.c or xhci.c).
> >
> > Signed-off-by: Ran Wang <ran.wang_1@....com>
> > Reviewed-by: Rob Herring <robh@...nel.org>
> [...]
> 
> MBR, Sergei