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

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Message-ID: <364d8916-5630-9662-1f39-fd18f84d1941@caviumnetworks.com>
Date:   Mon, 29 Oct 2018 05:21:24 +0000
From:   George Cherian <gcherian@...iumnetworks.com>
To:     Alan Stern <stern@...land.harvard.edu>,
        "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


Hi Alan,

Thanks for the review.
I will update the patch accordingly and send out v2.

On 10/28/2018 10:48 PM, Alan Stern wrote:
> 
> 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
> 
Regards,
-George