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Subject: Re: [RESEND][PATCH v3 1/2] usb: dwc3: Add avoiding vbus glitch happen
 during xhci reset
To:     Ran Wang <ran.wang_1@nxp.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Felipe Balbi <balbi@kernel.org>, Yang Li <pku.leo@gmail.com>
Cc:     linux-usb@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20190606025418.26313-1-ran.wang_1@nxp.com>
From:   Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Message-ID: <78eb1558-b8d4-0632-ad0c-4144c711d2da@cogentembedded.com>
Date:   Thu, 6 Jun 2019 11:16:54 +0300
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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. :-)

> 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@nxp.com>
> Reviewed-by: Rob Herring <robh@kernel.org>
[...]

MBR, Sergei