linux-kernel - Re: [BACKPORT 4.14.y 04/18] usb: dwc3: Allow disabling of metastability workaround

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Date:   Wed, 11 Sep 2019 08:01:40 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Greg KH <greg@...ah.com>
Cc:     "# 4 . 7" <stable@...r.kernel.org>, linux-usb@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-pm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-omap@...r.kernel.org, linux-i2c@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-mtd@...ts.infradead.org
Subject: Re: [BACKPORT 4.14.y 04/18] usb: dwc3: Allow disabling of
 metastability workaround

On Tue, 10 Sep 2019 at 08:36, Greg KH <greg@...ah.com> wrote:
>
> On Thu, Sep 05, 2019 at 10:17:45AM -0600, Mathieu Poirier wrote:
> > From: Roger Quadros <rogerq@...com>
> >
> > commit 42bf02ec6e420e541af9a47437d0bdf961ca2972 upstream
> >
> > Some platforms (e.g. TI's DRA7 USB2 instance) have more trouble
> > with the metastability workaround as it supports only
> > a High-Speed PHY and the PHY can enter into an Erratic state [1]
> > when the controller is set in SuperSpeed mode as part of
> > the metastability workaround.
> >
> > This causes upto 2 seconds delay in enumeration on DRA7's USB2
> > instance in gadget mode.
> >
> > If these platforms can be better off without the workaround,
> > provide a device tree property to suggest that so the workaround
> > is avoided.
> >
> > [1] Device mode enumeration trace showing PHY Erratic Error.
> >      irq/90-dwc3-969   [000] d...    52.323145: dwc3_event: event (00000901): Erratic Error [U0]
> >      irq/90-dwc3-969   [000] d...    52.560646: dwc3_event: event (00000901): Erratic Error [U0]
> >      irq/90-dwc3-969   [000] d...    52.798144: dwc3_event: event (00000901): Erratic Error [U0]
>
> Does the DT also need to get updated with this new id for this?  Is that
> a separate patch somewhere?

The upstream commit is:

b8c9c6fa2002 ARM: dts: dra7: Disable USB metastability workaround for USB2

Should I just send the latter or you prefer a resend with both patches?

Thanks,
Mathieu

>
> thanks,
>
> greg k-h