linux-kernel - Re: [PATCH v2 1/2] usb: dwc3: Add avoiding vbus glitch happen during xhci reset

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Date:   Fri, 22 Feb 2019 14:34:59 -0600
From:   Rob Herring <robh@...nel.org>
To:     Ran Wang <ran.wang_1@....com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "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>,
        Ran Wang <ran.wang_1@....com>
Subject: Re: [PATCH v2 1/2] usb: dwc3: Add avoiding vbus glitch happen during
 xhci  reset

On Tue, 19 Feb 2019 07:23:14 +0000, 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
> 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>
> ---
> Changes in v2:
>   - Correct typos
>   - Shorten the name to snps,host-vbus-glitches
> 
>  Documentation/devicetree/bindings/usb/dwc3.txt |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 

Reviewed-by: Rob Herring <robh@...nel.org>