linux-kernel - Re: [PATCH] xhci: Add quirk to workaround the errata seen on Cavium Thunder-X2 Soc

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Date:   Sun, 28 Oct 2018 13:18:33 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     "Cherian, George" <George.Cherian@...ium.com>
cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "mathias.nyman@...el.com" <mathias.nyman@...el.com>
Subject: Re: [PATCH] xhci: Add quirk to workaround the errata seen on Cavium
 Thunder-X2 Soc

On Sat, 27 Oct 2018, Cherian, George wrote:

> Implement workaround for ThunderX2 Errata-129 (documented in
> CN99XX Known Issues" available at Cavium support site).
> As per ThunderX2errata-129, USB-2.0 device may come up as USB-1.0
> If a connection to a USB-1.0 device is followed by another connection
> to a USB-2.0 device, the link will come up as USB-1.0 for the USB-2.0
> device.
> 
> Resolution: Reset the PHY after the USB1.0 device is disconnected.
> The PHY reset sequence is done using private registers in XHCI register
> space. After the PHY is reset we check for the PLL lock status and retry
> the operation if it fails. From our tests, retrying 4 times is sufficient.
> 
> Add a new quirk flag XHCI_RESET_PLL_ON_DISCONNECT to invoke the workaround
> in handle_xhci_port_status().

Minor nitpick (for both the patch description and the code comments):

USB 1.0 was never widely adopted and is not used any more.  The
earliest vesion of USB currently used in supported devices is USB 1.1.  
Likewise, there are a few devices around that support USB 2.1, not
USB 2.0, but they are presumably also subject to the problem described
above.

I suggest you change the description and the comments to refer to USB 1 
and USB 2 instead of USB 1.0 and USB 2.0, as the latter are too 
restrictive and misleading.

Alan Stern