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

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Date:   Tue, 10 Sep 2019 15:36:01 +0100
From:   Greg KH <greg@...ah.com>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     stable@...r.kernel.org, linux-usb@...r.kernel.org,
        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 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?

thanks,

greg k-h