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Date:   Thu, 6 Jun 2019 11:16:54 +0300
From:   Sergei Shtylyov <>
To:     Ran Wang <>,
        Greg Kroah-Hartman <>,
        Rob Herring <>,
        Mark Rutland <>,
        Felipe Balbi <>, Yang Li <>
Subject: Re: [RESEND][PATCH v3 1/2] usb: dwc3: Add avoiding vbus glitch happen
 during xhci reset


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. :-)

> 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 <>
> Reviewed-by: Rob Herring <>

MBR, Sergei

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