Re: [PATCH] xhci: Add quirk to workaround the errata seen on Cavium Thunder-X2 Soc
From: Alan Stern
Date: Sun Oct 28 2018 - 13:18:37 EST
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
> 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
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.